Terminal apparatus, base station apparatus and communication method

ABSTRACT

The present invention enables efficient transmission/reception of a signal including control information between a base station apparatus and a mobile station apparatus. To realize this, there are provided a receiver configured to receive an enhanced physical downlink control channel from the base station apparatus; a setting unit configured to be able to set, using at least a format of downlink control information included in the received enhanced physical downlink control channel, one of a plurality of possible sets of M, M being the number of first elements that constitute the enhanced physical downlink control channel; and a monitoring unit configured to monitor a search region in which the enhanced physical downlink control channel obtained on the basis of the set possible set of M is possibly mapped.

This application is a Continuation of U.S. application Ser. No.14/374,793 filed on Jul. 25, 2014, which is the National Phase of PCTInternational Application No. PCT/JP2013/050715 filed on Jan. 17, 2013,which claims the benefit of Japanese Application No. 2012-015018 filedin Japan on Jan. 27, 2012. The entire contents of all of the aboveapplications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a base station apparatus, a mobilestation apparatus, a communication method, an integrated circuit, and acommunication system with which, in a communication system including aplurality of mobile station apparatuses and a base station apparatus, aregion in which signals including control information are possiblymapped can be efficiently configured, a base station apparatus iscapable of efficiently transmitting signals including controlinformation to a mobile station apparatus, and the mobile stationapparatus is capable of efficiently receiving the signals including thecontrol information from the base station apparatus.

BACKGROUND ART

Evolution of radio access schemes and radio networks for cellular mobilecommunication (hereinafter referred to as “Long Term Evolution (LTE)” or“Evolved Universal Terrestrial Radio Access (SUTRA)”) has beenstandardized in the 3rd Generation Partnership Project (3GPP). In LTE,an orthogonal frequency division multiplexing (OFDM) scheme, which is amulti-carrier transmission scheme, is used as a communication scheme forwireless communication from a base station apparatus to a mobile stationapparatus (hereinafter referred to as downlink (DL)). Also, in LTE, asingle-carrier frequency division multiple access (SC-FDMA) scheme,which is a single-carrier transmission scheme, is used as acommunication scheme for wireless communication from a mobile stationapparatus to a base station apparatus (hereinafter referred to as uplink(UL)). In LTE, a discrete Fourier transform-spread OFDM (DFT-SpreadOFDM) scheme is used as an SC-FDMA scheme.

LTE-A (LTE-Advanced), which is a development of LTE and in which newtechnology is applied, has been studied. In LTE-A, support of at leastthe same channel structure as LTE is being discussed. A channel means amedium used to transmit a signal. A channel used in a physical layer isreferred to as a physical channel, and a channel used in a medium accesscontrol (MAC) layer is referred to as a logical channel. The types ofphysical channels include a physical downlink shared channel (PDSCH)used to transmit and receive downlink data and control information, aphysical downlink control channel (PDCCH) used to transmit and receivedownlink control information, a physical uplink shared channel (PDSCH)used to transmit and receive uplink data and control information, aphysical uplink control channel (PUCCH) used to transmit and receivecontrol information, a synchronization channel (SCH) used to establishdownlink synchronization, a physical random access channel (PRACH) usedto establish uplink synchronization, a physical broadcast channel (PBCH)used to transmit downlink system information, and so forth. A mobilestation apparatus or a base station apparatus maps signals generatedfrom control information, data, or the like to respective physicalchannels, and transmits the signals. Data transmitted on the physicaldownlink shared channel or the physical uplink shared channel isreferred to as a transport block.

Control information mapped to the physical uplink control channel isreferred as uplink control information (UCI). The uplink controlinformation is control information (a receive confirmationacknowledgement; ACK/NACK) representing a positive acknowledgement (ACK)or a negative acknowledgement (NACK) for received data mapped to thephysical downlink shared channel, control information (SchedulingRequest: SR) representing a request for assignment of uplink resources,or control information (Channel Quality Indicator: CQI) representingdownlink reception quality (also referred to as channel quality).

<Coordinated Communication>

In LTE-A, to reduce or suppress interference experienced by a mobilestation apparatus in a cell edge area, or to increase the receive signalpower, intercell coordinated communication (Cooperative Multipoint: CoMPcommunication) in which adjacent cells cooperatively communicate witheach other is being discussed. For example, a form in which a basestation apparatus communicates using an arbitrary single frequency bandis referred to as a “cell”. For example, a method in which weightingsignal processing (precoding processing) that differs among a pluralityof cells is applied to a signal, and a plurality of base stationapparatuses coordinate with each other to transmit the signal to thesame mobile station apparatus (also referred to as Joint Processing orJoint Transmission) and so forth are being discussed as intercellcoordinated communication. With this method, the signal power tointerference plus noise power ratio of a mobile station apparatus can beenhanced, and the reception performance in the mobile station apparatuscan be improved. For example, a method in which a plurality of cellscoordinate with each other to perform scheduling for a mobile stationapparatus (Coordinated Scheduling: CS) is being discussed as intercellcoordinated communication. With this method, the signal power tointerference plus noise power ratio of a mobile station apparatus can beenhanced. For example, a method in which a plurality of cells coordinatewith each other to transmit a signal to a mobile station apparatus byapplying beamforming (Coordinated beamforming: CB) is being discussed asintercell coordinated communication. With this method, the signal powerto interference plus noise power ratio of a mobile station apparatus canbe enhanced. For example, a method in which a signal is transmittedusing a certain resource in only one cell and a signal is nottransmitted using a certain resource in one cell (Blanking, Muting) isbeing discussed as intercell coordinated communication. With thismethod, the signal power to interference plus noise power ratio of amobile station apparatus can be enhanced.

Regarding a plurality of cells used in coordinated communication,different cells may be configured by different base station apparatuses,different cells may be configured by different RRHs (Remote Radio Heads,an outdoor radio unit smaller than a base station apparatus; alsoreferred to as a Remote Radio Unit: RRU) managed by the same basestation apparatus, different cells may be configured by a base stationapparatus and an RRH managed by the base station apparatus, anddifferent cells may be configured by a base station apparatus and an RRHmanaged by another base station apparatus different from the basestation apparatus.

A base station apparatus with wide coverage is generally referred to asa macro base station apparatus. A base station apparatus with narrowcoverage is generally referred to as a pico base station apparatus or afemto base station apparatus. For RRHs, operation in areas of narrowercoverage than of macro base station apparatuses is being discussed. Adeployment such as a communication system which includes a macro basestation apparatus and an RRH, and in which the coverage supported by themacro base station apparatus includes part or all of the coveragesupported by the RRH, is referred to as a heterogeneous networkdeployment. In a communication system with such a heterogeneous networkdeployment, a method in which a macro base station apparatus and an RRHcoordinate with each other to transmit a signal to a mobile stationapparatus located in a mutually overlapping coverage area is beingdiscussed. Here, the RRH is managed by the macro base station apparatus,and transmission/reception is controlled. The macro base stationapparatus and the RRH are connected to each other by a wired link suchas an optical fiber, or by a wireless link using a relay technology. Inthis way, the macro base station apparatus and the RRH performcoordinated communication using some or all of the same radio resources,and accordingly overall frequency utilization efficiency (transmissioncapacity) can be increased within the area of coverage constructed bythe macro base station apparatus.

In the case of being located near a macro base station apparatus or anRRH, a mobile station apparatus is capable of performing single-cellcommunication with the macro base station apparatus or the RRH. In otherwords, a certain mobile station apparatus communicates with a macro basestation apparatus or an RRH without using coordinated communication totransmit or receive a signal. For example, the macro base stationapparatus receives an uplink signal from a mobile station apparatus thatis close in distance to the macro base station apparatus. For example,the RRH receives an uplink signal from a mobile station apparatus thatis close in distance to the RRH. Furthermore, in a case where the mobilestation apparatus is located near an edge of coverage constructed by theRRH (cell edge), countermeasures against the same channel interferencefrom the macro base station apparatus is necessary. For multi-cellcommunication (coordinated communication) between a macro base stationapparatus and an RRH, a method for reducing or suppressing interferenceexperienced by a mobile station apparatus in a cell edge area by using aCoMP scheme in which adjacent base station apparatuses coordinate witheach other is being discussed.

Also, it is discussed that a mobile station apparatus receives signalstransmitted from both a macro base station apparatus and an RRH usingcoordinated communication in the downlink, and transmits a signal to anyone of the macro base station apparatus and the RRH in an appropriateform in the uplink. For example, the mobile station apparatus transmitsan uplink signal with transmit power that is suitable for the macro basestation apparatus to receive the signal. For example, the mobile stationapparatus transmits an uplink signal with transmit power that issuitable for the RRH to receive the signal. Accordingly, unnecessaryinterference in the uplink can be reduced, and the frequency utilizationefficiency can be enhanced.

It is necessary for a mobile station apparatus to obtain, regarding aprocess of receiving a data signal, control information representing amodulation scheme to be used for the data signal, a coding rate, aspatial multiplexing number, a transmit power adjustment value,assignment of resources, and so forth. In LTE-A, introduction of a newcontrol channel for transmitting control information regarding a datasignal is being discussed (NPL 1). For example, improvement of thecapacity of the entire control channel is being discussed. For example,support of interference coordination in the frequency domain for a newcontrol channel is being discussed. For example, support of spatialmultiplexing for a new control channel is being discussed. For example,support of beamforming for a new control channel is being discussed. Forexample, support of diversity for a new control channel is beingdiscussed. For example, use of a new control channel in a new type ofcarrier is being discussed. For example, not transmitting a referencesignal common to all mobile station apparatuses in a cell in a new typeof carrier is being discussed. For example, reducing the frequency oftransmitting a reference signal common to all mobile station apparatusesin a cell in a new type of carrier to be lower than in a conventionaltechnology is being discussed. For example, demodulating a signal suchas control information using a reference signal specific to a mobilestation apparatus in a new type of carrier is being discussed.

For example, applying coordinated communication and multi-antennatransmission for a new control channel as application of beamforming isbeing discussed. Specifically, it is discussed that a plurality of basestation apparatuses and a plurality of RRHs compatible with LTE-A applyprecoding processing for a signal on a new control channel, and the sameprecoding processing is applied to a reference signal (RS) fordemodulating the signal on the new control channel. Specifically, it isdiscussed that a plurality of base station apparatuses and a pluralityof RRHs compatible with LTE-A map, in the region of resources where aPDSCH is mapped in LTE, a signal on a new control channel and an RS towhich the same precoding processing is applied, and transmit the signaland RS. It is discussed that a mobile station apparatus compatible withLTE-A demodulates the signal on the new control channel subjected toprecoding processing using the RS that has been received and subjectedto the same precoding processing, and obtains control information. Withthis method, it is not necessary to transmit and receive informationregarding the precoding processing applied to a signal on a new controlchannel between a base station apparatus and a mobile station apparatus.

For example, as application of diversity, a method for obtaining aneffect of frequency diversity by forming a signal on a new controlchannel using resources separated in the frequency domain is beingdiscussed. On the other hand, a method for forming a signal on a newcontrol channel using resources not separated in the frequency domain ina case where beamforming is applied to the new control channel is beingdiscussed.

For example, as support of spatial multiplexing, application of MU-MIMO(Multi User-Multi Input Multi Output) in which control channels fordifferent mobile station apparatuses are multiplexed on the sameresource is being discussed.

Specifically, it is discussed that a base station apparatus transmitsreference signals that are orthogonal to each other between differentmobile station apparatuses and transmits signals on different newcontrol channels by spatially multiplexing the signals on a commonresource. For example, spatial multiplexing of signals on different newcontrol channels is realized by applying appropriate beamforming(precoding processing) to each of the signals on the different newcontrol channels.

CITATION LIST Non Patent Literature

-   NPL 1: 3GPP TSG RANI #66bis, Zhuhai, China, 10-14, October, 2011,    R1-113589 “Way Forward on downlink control channel enhancements by    UE-specific RS”

SUMMARY OF INVENTION Technical Problem

It is desirable that a control channel be transmitted and received withefficient use of resources. An amount of resources satisfyingrequirements for each mobile station apparatus is necessary for thecontrol channel. If resources are not efficiently used for the controlchannel, the capacity of the control channel cannot be increased, andthe number of mobile station apparatuses to which the control channel isassigned cannot be increased.

For example, it is desirable that an increase in capacity of controlchannels of an entire system be efficiently controlled by flexiblyconfiguring, with a base station apparatus, resource block pairs to beused by a terminal apparatus.

The present invention has been made in view of the above-describedpoints, and an object of the invention relates to a communicationsystem, a mobile station apparatus, a base station apparatus, acommunication method, and an integrated circuit with which, in acommunication system including a plurality of mobile station apparatusesand a base station apparatus, a region in which signals includingcontrol information are possibly mapped can be efficiently configured, abase station apparatus is capable of efficiently transmitting signalsincluding control information to a mobile station apparatus, and themobile station apparatus is capable of efficiently receiving the signalsincluding the control information from the base station apparatus.

Solution to Problem

(1) To achieve the above-described object, the present invention takesthe following measures. That is, a base station apparatus of the presentinvention is a base station apparatus that communicates with a mobilestation apparatus, and includes a controller configured to be able toset, on the basis of a format of downlink control information to betransmitted to the mobile station, one of a plurality of possible setsof M, M being the number of first elements that constitute an enhancedphysical downlink control channel; and a transmitter configured totransmit the downlink control information to the mobile station by usingthe enhanced physical downlink control channel constituted by the Mfirst elements, a value of M being included in the one set. A resourceblock pair is constituted by a plurality of resource elements. Theenhanced physical downlink control channel is formed using at least apart of one or a plurality of the resource block pairs. A second elementis formed by dividing at least a part of the resource block pair in N (Nis a natural number). Each of the first elements is formed using aplurality of the second elements.

(2) In the base station apparatus of the present invention, the enhancedphysical downlink control channel is configured for localizedtransmission.

(3) In the communication base station apparatus of the presentinvention, the enhanced physical downlink control channel is configuredfor distributed transmission.

(4) In the base station apparatus of the present invention, theplurality of possible sets of M include a first set and a second set,the second set includes a value larger than any values included in thefirst set, and the first set includes a value smaller than any valuesincluded in the second set.

(5) In the base station apparatus of the present invention, the firstset and the second set include the same number of values.

(6) A mobile station apparatus of the present invention is a mobilestation apparatus that communicates with a base station apparatus, andincludes a receiver configured to receive an enhanced physical downlinkcontrol channel from the base station apparatus; a setting unitconfigured to be able to set, using at least a format of downlinkcontrol information included in the received enhanced physical downlinkcontrol channel, one of a plurality of possible sets of M, M being thenumber of first elements that constitute the enhanced physical downlinkcontrol channel; and a monitoring unit that monitors a search region inwhich the enhanced physical downlink control channel obtained on thebasis of the set possible set of M is possibly mapped. A resource blockpair is constituted by a plurality of resource elements. The enhancedphysical downlink control channel is formed using at least a part of oneor a plurality of the resource block pairs. A second element is formedby dividing at least a part of the resource block pair in N (N is anatural number). Each of the first elements is formed using a pluralityof the second elements.

(7) In the mobile station apparatus of the present invention, theenhanced physical downlink control channel is configured for localizedtransmission.

(8) In the mobile station apparatus of the present invention, theenhanced physical downlink control channel is configured for distributedtransmission.

(9) In the mobile station apparatus of the present invention, theplurality of possible sets of M include a first set and a second set,the second set includes a value larger than any values included in thefirst set, and the first set includes a value smaller than any valuesincluded in the second set.

(10) In the mobile station apparatus of the present invention, the firstset and the second set include the same number of values.

(11) A communication method used for a base station apparatus of thepresent invention is a communication method used for a base stationapparatus that communicates with a mobile station apparatus. Thecommunication method includes a step of setting, on the basis of aformat of downlink control information to be transmitted to the mobilestation, one of a plurality of possible sets of M as needed, M being thenumber of first elements that constitute an enhanced physical downlinkcontrol channel; and a step of transmitting the downlink controlinformation to the mobile station by using the enhanced physicaldownlink control channel constituted by the M first elements, a value ofM being included in the one set. A resource block pair is constituted bya plurality of resource elements. The enhanced physical downlink controlchannel is formed using at least a part of one or a plurality of theresource block pairs. A second element is formed by dividing at least apart of the resource block pair in N (N is a natural number). Each ofthe first elements is formed using a plurality of the second elements.

(12) A communication method used for a mobile station apparatus of thepresent invention is a communication method used for a mobile stationapparatus that communicates with a base station apparatus. Thecommunication method includes a step of receiving an enhanced physicaldownlink control channel from the base station apparatus; a step ofsetting, using at least a format of downlink control informationincluded in the received enhanced physical downlink control channel, oneof a plurality of possible sets of M as needed, M being the number offirst elements that constitute the enhanced physical downlink controlchannel; and a step of monitoring a search region in which the enhancedphysical downlink control channel obtained on the basis of the setpossible set of M is possibly mapped. A resource block pair isconstituted by a plurality of resource elements. The enhanced physicaldownlink control channel is formed using at least a part of one or aplurality of the resource block pairs. A second element is formed bydividing at least a part of the resource block pair in N (N is a naturalnumber). Each of the first elements is formed using a plurality of thesecond elements.

(13) An integrated circuit used for a base station apparatus of thepresent invention has a function of being able to set, on the basis of aformat of downlink control information to be transmitted to the mobilestation, one of a plurality of possible sets of M, M being the number offirst elements that constitute an enhanced physical downlink controlchannel; and a function of transmitting the downlink control informationto the mobile station by using the enhanced physical downlink controlchannel constituted by the M first elements, a value of M being includedin the one set. A resource block pair is constituted by a plurality ofresource elements. The enhanced physical downlink control channel isformed using at least a part of one or a plurality of the resource blockpairs. A second element is formed by dividing at least a part of theresource block pair in N (N is a natural number). Each of the firstelements is formed using a plurality of the second elements.

(14) An integrated circuit used for a mobile station apparatus of thepresent invention is an integrated circuit used for a mobile stationapparatus that communicates with a base station apparatus. Theintegrated circuit has a function of receiving an enhanced physicaldownlink control channel from the base station apparatus; a function ofbeing able to set, using at least a format of downlink controlinformation included in the received enhanced physical downlink controlchannel, one of a plurality of possible sets of M, M being the number offirst elements that constitute the enhanced physical downlink controlchannel; and a function of monitoring a search region in which theenhanced physical downlink control channel obtained on the basis of theset possible set of M is possibly mapped. A resource block pair isconstituted by a plurality of resource elements. The enhanced physicaldownlink control channel is formed using at least a part of one or aplurality of the resource block pairs. A second element is formed bydividing at least a part of the resource block pair in N (N is a naturalnumber). Each of the first elements is formed using a plurality of thesecond elements.

(15) A communication system of the present invention is a communicationsystem in which a mobile station apparatus and a base station apparatuscommunicate with each other using an enhanced physical downlink controlchannel. The base station apparatus is configured to set, on the basisof a format of downlink control information to be transmitted to themobile station apparatus, one of a plurality of possible sets of M asneeded, M being the number of first elements that constitute theenhanced physical downlink control channel, and transmit the downlinkcontrol information to the mobile station by using the enhanced physicaldownlink control channel constituted by the M first elements, a value ofM being included in the one set. The mobile station apparatus isconfigured to receive the enhanced physical downlink control channel,set, using at least a format of the downlink control informationincluded in the enhanced physical downlink control channel, one of aplurality of possible sets of M as needed, M being the number of firstelements that constitute the enhanced physical downlink control channel,and monitor a search region in which the enhanced physical downlinkcontrol channel obtained on the basis of the set possible set of M ispossibly mapped. A resource block pair is constituted by a plurality ofresource elements. The enhanced physical downlink control channel isformed using at least a part of one or a plurality of the resource blockpairs. A second element is formed by dividing at least a part of theresource block pair in N (N is a natural number). Each of the firstelements is formed using a plurality of the second elements.

In this description, the present invention is disclosed in the point ofimproving a communication system in which a region where a controlchannel is possibly mapped is configured for a mobile station apparatusby a base station apparatus, a mobile station apparatus, a base stationapparatus, a communication method, and an integrated circuit. Thecommunication scheme to which the present invention is applicable is notlimited to a communication scheme such as LTE or LTE-A having upwardcompatibility with LTE. For example, the present invention is alsoapplicable to a UMTS (Universal Mobile Telecommunications System).

Advantageous Effects of Invention

According to the present invention, a base station apparatus is capableof efficiently transmitting a signal including control information to amobile station apparatus, the mobile station apparatus is capable ofefficiently receiving the signal including the control information fromthe base station apparatus, and a more efficient communication systemcan be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram illustrating the configuration of abase station apparatus 3 according to an embodiment of the presentinvention.

FIG. 2 is a schematic block diagram illustrating the configuration of atransmission processor 107 of the base station apparatus 3 according tothe embodiment of the present invention.

FIG. 3 is a schematic block diagram illustrating the configuration of areception processor 101 of the base station apparatus 3 according to theembodiment of the present invention.

FIG. 4 is a schematic block diagram illustrating the configuration of amobile station apparatus 5 according to the embodiment of the presentinvention.

FIG. 5 is a schematic block diagram illustrating the configuration of areception processor 401 of the mobile station apparatus 5 according tothe embodiment of the present invention.

FIG. 6 is a schematic block diagram illustrating the configuration of atransmission processor 407 of the mobile station apparatus 5 accordingto the embodiment of the present invention.

FIG. 7 is a flowchart illustrating an example of a process related tosetting of UE-specific RSs used to demodulate individual E-CCEs in a DLPRB pair in a second PDCCH region in the mobile station apparatus 5according to the embodiment of the present invention.

FIG. 8 is a flowchart illustrating an example of a process related tosetting of transmit antennas (antenna ports) used to transmit individualE-CCEs in a DL PRB pair in a second PDCCH region in the base stationapparatus 3 according to the embodiment of the present invention.

FIG. 9 is a diagram schematically illustrating the overview of acommunication system according to the embodiment of the presentinvention.

FIG. 10 is a diagram schematically illustrating the configuration of adownlink time frame from the base station apparatus 3 or an RRH 4 to themobile station apparatus 5 according to the embodiment of the presentinvention.

FIG. 11 is a diagram illustrating an example of mapping of downlinkreference signals in a downlink subframe in the communication system 1according to the embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of mapping of downlinkreference signals in a downlink subframe in the communication system 1according to the embodiment of the present invention.

FIG. 13 is a diagram illustrating a DL PRB pair to which CSI-RSs(channel state information reference signals) for eight antenna portsare mapped.

FIG. 14 is a diagram schematically illustrating the configuration of anuplink time frame from the mobile station apparatus 5 to the basestation apparatus 3 or the RRH 4 according to the embodiment of thepresent invention.

FIG. 15 is a diagram illustrating a logical relationship between a firstPDCCH and CCEs in the communication system 1 according to the embodimentof the present invention.

FIG. 16 is a diagram illustrating an example of arrangement of resourceelement groups in a downlink radio frame in the communication system 1according to the embodiment of the present invention.

FIG. 17 is a diagram schematically illustrating the configuration ofregions where second PDCCHs are possibly mapped in the communicationsystem 1 according to the embodiment of the present invention.

FIG. 18 is a diagram illustrating a logical relationship between asecond PDCCH and E-CCEs in the communication system 1 according to theembodiment of the present invention.

FIG. 19 is a diagram illustrating an example of the configuration ofE-CCEs according to the embodiment of the present invention.

FIG. 20 is a diagram illustrating an example of the configuration ofE-CCEs according to the embodiment of the present invention.

FIG. 21 is a diagram illustrating an example of the configuration ofE-CCEs, regions, and Localized E-PDCCH.

FIG. 22 is a diagram illustrating an example of the configuration ofE-CCEs, regions, and Distributed E-PDCCH.

FIG. 23 is a diagram illustrating an example of the configuration ofE-CCEs, regions, and Localized E-PDCCH.

FIG. 24 is a diagram illustrating an example of the configuration ofE-CCEs, regions, a bitmap, PRB pairs, and Distributed E-PDCCH (the basestation apparatus side).

FIG. 25 is a diagram illustrating an example of the configuration ofE-CCEs, regions, a bitmap, PRB pairs, and Distributed E-PDCCH (themobile station apparatus side).

FIG. 26 is a diagram illustrating an example of the configuration ofE-CCEs, regions, a bitmap, PRB pairs, and Distributed E-PDCCH (the basestation apparatus side).

FIG. 27 is a diagram illustrating an example of the configuration ofE-CCEs, regions, a bitmap, PRB pairs, and Distributed E-PDCCH (themobile station apparatus side).

FIG. 28 is a diagram illustrating an example of the configuration ofE-CCEs, regions, a bitmap, PRB pairs, and Distributed E-PDCCH (the basestation apparatus side).

FIG. 29 is a diagram illustrating monitoring of second PDCCHs in themobile station apparatus 5 according to the embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

The technology described in this description can be used in variouswireless communication systems, such as a code division multiple access(CDMA) system, a time division multiple access (TDMA) system, afrequency division multiple access (FDMA) system, an orthogonal FDMA(OFDMA) system, a single-carrier FDMA (SC-FDMA) system, and othersystems. The terms “system” and “network” can be often usedsynonymously. A CDMA system can be compatible with radio technologies(standards), such as universal terrestrial radio access (UTRA) andcdma2000 (registered trademark). UTRA includes wideband CDMA (WCDMA) andother improvements of CDMA. cdma2000 covers the standards of IS-2000,IS-95, and IS-856. A TDMA system can be compatible with a radiotechnology such as Global System for Mobile Communications (GSM(registered trademark)). An OFDMA system can be compatible with radiotechnologies, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband(UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andFlash-OFDM (registered trademark). UTRA and E-UTRA correspond to part ofuniversal mobile telecommunications system (UMTS). 3GPP LTE (Long TermEvolution) is UMTS that uses E-UTRA in which OFDMA is adopted in thedownlink and SC-FDMA is adopted in the uplink. LTE-A is a system, radiotechnology, and standard achieved by improving LTE. UTRA, E-UTRA, UMTS,LTE, LTE-A, and GSM are described in documents issued by an organizationcalled 3rd Generation Partnership Project (3GPP). cdma2000 and UMB aredescribed in documents issued by an organization called 3rd GenerationPartnership Project 2 (3GPP2). For clarity, an aspect of the presenttechnology will be described below regarding data communication in LTEand LTE-A, and terms related to LTE and LTE-A will be used in manyplaces of the following description.

Hereinafter, an embodiment of the present invention will be described indetail with reference to the drawings. The overview of a communicationsystem and the configuration of a radio frame according to theembodiment will be described with reference to FIGS. 9 to 26. Theconfiguration of the communication system according to the embodimentwill be described with reference to FIGS. 1 to 6. Operation processes ofthe communication system according to the embodiment will be describedwith reference to FIGS. 7 and 8.

FIG. 9 is a diagram schematically illustrating the overview of thecommunication system according to the embodiment of the presentinvention. In the communication system 1 illustrated in FIG. 9, a basestation apparatus (eNodeB, NodeB, BS: Base Station, AP: Access Point,also referred to as a macro base station) 3, a plurality of RRHs (RemoteRadio Heads, devices including an outdoor radio unit smaller than a basestation apparatus, also referred to as Remote Radio Units: RRUs) (alsoreferred to as remote antennas or distributed antennas) 4A, 4B, and 4C,and a plurality of mobile station apparatuses (also referred to as UE:User Equipment, MS: Mobile Stations, MT: Mobile Terminals, terminals,terminal devices, or mobile terminals) 5A, 5B, and 5C communicate withone another. In the embodiment, a description will be given below asappropriate, with each of the RRHs 4A, 4B, and 4C being referred to asan RRH 4, and each of the mobile station apparatuses 5A, 5B, and 5Cbeing referred to as a mobile station apparatus 5. In the communicationsystem 1, the base station apparatus 3 and the RRH 4 coordinate witheach other to communicate with the mobile station apparatus 5. In FIG.9, the base station apparatus 3 and the RRH 4A perform coordinatedcommunication with the mobile station apparatus 5A, the base stationapparatus 3 and the RRH 4B perform coordinated communication with themobile station apparatus 5B, and the base station apparatus 3 and theRRH 4C perform coordinated communication with the mobile stationapparatus 5C.

An RRH may be called a specific form of a base station apparatus.Specifically, an RRH may be called a base station apparatus whichincludes only a signal processor, and in which a parameter to be used inthe RRH is set by and scheduling is determined by another base stationapparatus. Therefore, in the following description, it should be notedthat the expression “base station apparatus 3” includes the RRH 4 asappropriate.

<Coordinated Communication>

In the communication system 1 according to the embodiment of the presentinvention, coordinated communication (Cooperative Multipoint: CoMPcommunication) in which a signal is transmitted and receivedcooperatively using a plurality of cells can be used. For example, aform in which a base station apparatus performs communication using anarbitrary single frequency band is referred to as a “cell”. For example,in coordinated communication, weighting signal processing (precodingprocessing) that differs among a plurality of cells (the base stationapparatus 3 and the RHH 4) is applied to a signal, and the base stationapparatus 3 and the RRH 4 coordinate with each other to transmit thesignal to the same mobile station apparatus 5 (Joint Processing, JointTransmission). For example, in coordinated communication, a plurality ofcells (the base station apparatus 3 and the RRH 4) coordinate with eachother to perform scheduling for the mobile station apparatus 5(Coordinated Scheduling: CS). For example, in coordinated communication,a plurality of cells (the base station apparatus 3 and the RRH 4)coordinate with each other to transmit a signal to the mobile stationapparatus 5 by applying beamforming (Coordinated Beamforming: CB). Forexample, in coordinated communication, only one of cells (the basestation apparatus 3 or the RRH 4) transmits a signal using a certainresource, and the other cell (the base station apparatus 3 or the RRH 4)does not transmit a signal using a certain resource (Blanking, Muting).

Although a description is omitted in the embodiment of the presentinvention, regarding a plurality of cells used in coordinatedcommunication, different cells may be configured by different basestation apparatuses 3, different cells may be configured by differentRRHs 4 managed by the same base station apparatus 3, or different cellsmay be configured by a base station apparatus 3 and an RRH 4 managed byanother base station apparatus 3 different from the base stationapparatus 3.

A plurality of cells are physically used as different cells, and may belogically used as the same cell. Specifically, a common cell identifier(physical cell ID) may be used for individual cells. A configuration inwhich a plurality of transmission apparatuses (the base stationapparatus 3 and the RRH 4) transmit a common signal to the samereception apparatus using the same frequency band is referred to as asingle frequency network (SFN).

It is assumed that the deployment of the communication system 1according to the embodiment of the present invention is a heterogeneousnetwork deployment. The communication system 1 includes the base stationapparatus 3 and the RRHs 4, and the coverage supported by the basestation apparatus 3 includes part or all of the coverage supported bythe RRHs 4. Here, “coverage” means an area in which communication can beperformed with requirements being satisfied. In the communication system1, the base station apparatus 3 and the RRH 4 coordinate with each otherto transmit a signal to the mobile station apparatus 5 located in amutually overlapping coverage. Here, the RRH 4 is managed by the basestation apparatus 3, and transmission and reception are controlled. Thebase station apparatus 3 and the RRH 4 are connected to each other by awired link such as an optical fiber or a wireless link using a relaytechnology.

In the case of being located near the base station apparatus 3 or theRRH 4, the mobile station apparatus 5 may perform single-cellcommunication with the base station apparatus 3 or the RRH 4. That is, acertain mobile station apparatus 5 may communicate with the base stationapparatus 3 or the RRH 4 without using coordinated communication, so asto transmit or receive a signal. For example, the base station apparatus3 may receive an uplink signal from the mobile station apparatus 5 thatis close in distance to the base station apparatus 3. For example, theRRH 4 may receive an uplink signal from the mobile station apparatus 5that is close in distance to the RRH 4. Also, for example, both the basestation apparatus 3 and the RRH 4 may receive an uplink signal from themobile station apparatus 5 located near an edge of the coverageconstructed by the RRH 4 (cell edge).

The mobile station apparatus 5 may receive signals transmitted from boththe base station apparatus 3 and the RRH 4 using coordinatedcommunication in the downlink, and may transmit a signal to any one ofthe base station apparatus 3 and the RRH 4 in an appropriate form in theuplink. For example, the mobile station apparatus 5 transmits an uplinksignal with transmit power appropriate for the base station apparatus 3to receive the signal. For example, the mobile station apparatus 5transmits an uplink signal with transmit power appropriate for the RRH 4to receive the signal.

In the embodiment of the present invention, MU (Multi-User)-MIMO can beapplied within a single base station apparatus 3. For example, MU-MIMOis a technology in which beam control is performed, using a precodingtechnology or the like, on signals addressed to a plurality of mobilestation apparatuses 5 that exist in different areas (for example, area Aand area B) in the area covered by the base station apparatus 3 thatuses a plurality of transmit antennas, and thereby the signals addressedto the mobile station apparatuses 5 are kept orthogonal to each other orco-channel interference is reduced even if the same resource is used inthe frequency domain and the time domain. MU-MIMO is also called SDMA(Space Division Multiple Access) because it spatially demultiplexessignals addressed to the mobile station apparatuses 5.

In MU-MIMO, the base station apparatus 3 transmits UE-specific RSs thatare orthogonal to each other between different mobile stationapparatuses 5, and transmits signals of different second PDCCHs byspatially multiplexing the signals on a common resource. In MU-MIMO,different precoding processing operations are applied to individualmobile station apparatuses 5 for which spatial multiplexing isperformed. Within the area covered the base station apparatus 3,different precoding processing operations can be performed on the secondPDCCH and UE-specific RS of the mobile station apparatus 5 located inarea A and those of the mobile station apparatus 5 located in area B. Aregion where the second PDCCH is to be possibly mapped can beindependently configured for the mobile station apparatus 5 located inarea A and the mobile station apparatus 5 located in area B, andprecoding processing can be independently applied.

In the communication system 1, downlink (DL), which corresponds to acommunication direction from the base station apparatus 3 or the RRH 4to the mobile station apparatus 5, includes a downlink pilot channel, aphysical downlink control channel (PDCCH), and a physical downlinkshared channel (PDSCH). Coordinated communication is applied to or notapplied to the PDSCH. The PDCCH is made up of a first PDCCH and a secondPDCCH (E-PDCCH: Enhanced-PDCCH). The downlink pilot channel is made upof a first-type reference signal (CRS described below) used todemodulate the PDSCH and the first PDCCH, a second-type reference signal(UE-specific RS described below) used to demodulate the PDSCH and thesecond PDCCH, and a third-type reference signal (CSI-RS describedbelow).

From one point of view, the first PDCCH is a physical channel that usesthe same transmit port (antenna port, transmit antenna) as that for thefirst-type reference signal. The second PDCCH is a physical channel thatuses the same transmit port as that for the second-type referencesignal. The mobile station apparatus 5 demodulates a signal mapped tothe first PDCCH by using the first-type reference signal, anddemodulates a signal mapped to the second PDCCH by using the second-typereference signal. The first-type reference signal is common to all themobile station apparatuses 5 in a cell, is inserted into almost allresource blocks, and is usable by any mobile station apparatus 5. Thus,the first PDCCH can be demodulated by any mobile station apparatus 5. Onthe other hand, the second-type reference signal can be basicallyinserted into only assigned resource blocks. Precoding processing can beadaptively applied to the second-type reference signal, like data.

From one point of view, the first PDCCH is a control channel mapped toOFDM symbols to which the PDSCH is not mapped. The second PDCCH is acontrol channel mapped to OFDM symbols to which the PDSCH is mapped.From one point of view, the first PDCCH is a control channel to which asignal is basically mapped over all PRBs in the downlink system band(PRBs in the first slot), and the second PDCCH is a control channel towhich a signal is mapped over PRB pairs (PRBs) configured by the basestation apparatus 3 in the downlink system band. Although the detailswill be described below, from one point of view, signal configurationsof the first PDCCH and the second PDCCH are different from each other.For the first PDCCH, a CCE configuration described below is used as asignal configuration. For the second PDCCH, an E-CCE (Enhanced-CCE)(first element) configuration described below is used as a signalconfiguration. In other words, the smallest unit (element) of resourcesused for the configuration of one control channel differs between thefirst PDCCH and the second PDCCH. Each control channel includes one ormore smallest units.

In the communication system 1, uplink (UL), which corresponds to acommunication direction from the mobile station apparatus 5 to the basestation apparatus 3 or the RRH 4, includes a physical uplink sharedchannel (PUSCH), an uplink pilot channel (uplink reference signal; ULRS, SRS: Sounding Reference Signal, DM RS: Demodulation ReferenceSignal), and a physical uplink control channel (PUCCH). A channel meansa medium used to transmit a signal. A channel used in a physical layeris referred to as a physical channel, and a channel used in a mediumaccess control (MAC) layer is referred to as a logical channel.

The present invention can be applied to a communication system in a casewhere coordinated communication is applied to the downlink, for example,in a case where multi-antenna transmission is applied to the downlink.To simplify the description, a description will be given of a case wherecoordinated communication is not applied to the uplink, that is, a casewhere multi-antenna transmission is not applied to the uplink, but thepresent invention is not limited to such a case.

The PDSCH is a physical channel used to transmit and receive downlinkdata and control information (different from control informationtransmitted on the PDCCH). The PDCCH is a physical channel used totransmit and receive downlink control information (different fromcontrol information transmitted on the PDSCH). The PUSCH is a physicalchannel used to transmit and receive uplink data and control information(different from control information transmitted in the downlink). ThePUCCH is a physical channel used to transmit and receive uplink controlinformation (UCI). The types of UCI include a receive confirmationacknowledgement (ACK/NACK) representing a positive acknowledgement (ACK)or a negative acknowledgement (NACK) for downlink data on the PDSCH, ascheduling request (SR) representing whether or not assignment ofresources is to be requested, and so forth. Other types of physicalchannels include a synchronization channel (SCH) used to establishsynchronization in the downlink, a physical random access channel(PRACH) used to establish synchronization in the uplink, a physicalbroadcast channel (PBCH) used to transmit downlink system information(also referred to as SIB: System Information Block), and so forth. ThePDSCH is also used to transmit downlink system information.

The mobile station apparatus 5, the base station apparatus 3, or the RRH4 maps signals generated from control information, data, or the like toindividual physical channels, and transmits the signals. The datatransmitted on the PDSCH or PUSCH is referred to as a transport block.The area managed by the base station apparatus 3 or the RRH 4 is calleda cell.

<Configuration of Downlink Time Frame>

FIG. 10 is a diagram schematically illustrating the configuration of adownlink time frame from the base station apparatus 3 or the RRH 4 tothe mobile station apparatus 5 according to the embodiment of thepresent invention. In FIG. 10, the horizontal axis represents the timedomain and the vertical axis represents the frequency domain. A downlinktime frame is made up of a pair of resource blocks (RBs) (also referredto as physical resource blocks (PRBs)), the pair being referred to as aphysical resource block pair (PRB pair). Each PRB pair is a unit ofassignment of resources, and each RB has a frequency band and a timeband of predetermined widths in the downlink. One downlink PRB pair(referred to as a downlink physical resource block pair (DL PRB pair))is made up of two PRBs that are contiguous in the time domain in thedownlink (referred to as downlink physical resource blocks (DL PRBs)).

In FIG. 10, one DL PRB is made up of twelve subcarriers in the frequencydomain of the downlink (referred to as downlink subcarriers), and ismade up of seven OFDM (orthogonal frequency division multiplexing)symbols in the time domain. The system band of the downlink (referred toas a downlink system band) is a downlink communication band of the basestation apparatus 3 or the RRH 4. For example, the system bandwidth ofthe downlink (referred to as a downlink system bandwidth) has afrequency bandwidth of 20 MHz.

In the downlink system band, a plurality of DL PRBs (DL PRB pairs) aremapped on the basis of the downlink system bandwidth. For example, thedownlink system band having a frequency bandwidth of 20 MHz is made upof one hundred and ten DL PRBs (DL PRB pairs).

In the time domain illustrated in FIG. 10, there are a slot made up ofseven OFDM symbols (referred to as a downlink slot) and a subframe madeup of two downlink slots (referred to as a downlink subframe). A unitmade up of one downlink subcarrier and one OFDM symbol is referred to asa resource element (RE) (downlink resource element). In each downlinksubframe, at least a PDSCH used to transmit information data (alsoreferred to as a transport block), a first PDCCH used to transmitcontrol information for the PDSCH, and a second PDCCH used to transmitcontrol information for the PDSCH are mapped. In FIG. 10, the firstPDCCH is made up of the first to third OFDM symbols in the downlinksubframe, and the PDSCH and the second PDCCH are made up of the fourthto fourteenth OFDM symbols in the downlink subframe. The PDSCH and thesecond PDCCH are mapped to different DL PRB pairs. The number of OFDMsymbols constituting the first PDCCH and the number of OFDM symbolsconstituting the PDSCH and the second PDCCH may be changed for eachdownlink subframe. The number of OFDM symbols constituting the secondPDCCH may be fixed. For example, regardless of the number of OFDMsymbols constituting the first PDCCH and the number of OFDM symbolsconstituting the PDSCH, the second PDCCH may be made up of the fourth tofourteenth OFDM symbols of the downlink subframe.

Although not illustrated in FIG. 10, a downlink pilot channel used totransmit a reference signal (RS) of the downlink (referred to as adownlink reference signal) is mapped to a plurality of downlink resourceelements in a distributed manner. Here, a downlink reference signalincludes at least a first-type reference signal, a second-type referencesignal, and a third-type reference signal, which are different from oneanother. For example, a downlink reference signal is used to estimatechannel variations of the PDSCH and PDCCH (first PDCCH, second PDCCH).The first-type reference signal is used to demodulate the PDSCH and thefirst PDCCH, and is also referred to as a Cell specific RS (CRS). Thesecond-type reference signal is used to demodulate the PDSCH and thesecond PDCCH, and is also referred to as a UE-specific RS. For example,the third-type reference signal is used only to estimate channelvariations, and is also referred to as a Channel State Information RS(CSI-RS). The downlink reference signal is a signal that is known in thecommunication system 1. The number of downlink resource elementsconstituting the downlink reference signal may depend on the number oftransmit antennas (antenna ports) used by the base station apparatus 3and the RRH 4 to communicate with the mobile station apparatus 5.Hereinafter, a description will be given of a case where a CRS is usedas the first-type reference signal, a UE-specific RS is used as thesecond-type reference signal, and a CSI-RS is used as the third-typereference signal. The UE-specific RS can also be used to demodulate thePDSCH to which coordinated communication is applied and the PDSCH towhich coordinated communication is not applied. The UE-specific RS canalso be used to demodulate the second PDCCH to which coordinatedcommunication (precoding processing) is applied and the second PDCCH towhich coordinated communication is not applied.

To the PDCCH (the first PDCCH or the second PDCCH), a signal generatedfrom control information, such as information representing assignment ofDL PRB pairs to the PDSCH, information representing assignment of UL PRBpairs to the PUSCH, and information representing a mobile stationidentifier (referred to as a Radio Network Temporary Identifier: RNTI),a modulation scheme, a coding rate, a retransmission parameter, aspatial multiplexing number, a precoding matrix, and a transmit powercontrol command (TPC command), is mapped. The control informationincluded in the PDCCH is referred to as downlink control information(DCI). The DCI including information representing assignment of DL PRBpairs to the PDSCH is referred to as downlink assignment (DL assignment,also referred to as Downlink grant), and the DCI including informationrepresenting assignment of UL PRB pairs to the PUSCH is referred to asuplink grant (referred to as UL grant). The downlink assignment includesa transmit power control command for the PUCCH. The uplink assignmentincludes a transmit power control command for the PUSCH. One PDCCHincludes only information representing assignment of resources of onePDSCH or information representing assignment of resources of one PUSCH,and does not include information representing assignment of resources ofa plurality of PDSCHs or information representing assignment ofresources of a plurality of PUSCHs.

Furthermore, information to be transmitted on the PDCCH includes acyclic redundancy check (CRC) code. A detailed description will be givenof the relationship among DCI, RNTI, and CRC that are transmitted on thePDCCH. A CRC code is generated from DCI by using a predeterminedgenerator polynomial. Processing of exclusive OR (also referred to asscrambling) is performed on the generated CRC code by using an RNTI. Asignal generated by modulating a bit representing DCI and a bitgenerated through processing of exclusive OR performed on the CRC codeby using the RNTI (referred to as CRC masked by UE ID) is actuallytransmitted on the PDCCH.

The resource of the PDSCH is mapped to the same downlink subframe as thedownlink subframe to which the resource of the PDCCH including thedownlink assignment used to assign the resource of the PDSCH in the timedomain is mapped.

Mapping of downlink reference signals will be described. FIG. 11 is adiagram illustrating an example of mapping of downlink reference signalsin a downlink subframe in the communication system 1 according to theembodiment of the present invention. To simplify the description,mapping of downlink reference signals in a certain DL PRB pair will bedescribed with reference to FIG. 11. In a plurality of DL PRB pairs inthe downlink system band, the same mapping method is used.

Among the shaded downlink resource elements, R0 and R1 represent CRSsfor antenna ports 0 and 1, respectively. Here, an antenna port means alogical antenna used in signal processing. One antenna port may be madeup of a plurality of physical antennas. A plurality of physical antennasconstituting the same antenna port transmit the same signal. Within thesame antenna port, delay diversity or CDD (Cyclic Delay Diversity) maybe applied by using a plurality of physical antennas, but other signalprocessing cannot be used. Here, FIG. 11 illustrates a case where CRSscorrespond to two antenna ports. However, the communication systemaccording to the embodiment may correspond to a different number ofantenna ports. For example, a CRS corresponding to one antenna port orfour antenna ports may be mapped to downlink resources. The CRS can bemapped to all the DL PRB pairs in the downlink system band.

Among the shaded downlink resource elements, D1 represents a UE-specificRS. In the case of transmitting a UE-specific RS by using a plurality ofantenna ports, different codes are used by the individual antenna ports.That is, CDM (Code Division Multiplexing) is applied to the UE-specificRS. Here, regarding a UE-specific RS, the length of a code used in CDMand the number of downlink resource elements used for mapping may bechanged on the basis of the type of signal processing (the number ofantenna ports) used for a control signal or data signal to be mapped tothe DL PRB pair. FIG. 11 illustrates an example of mapping of aUE-specific RS in a case where the number of antenna ports used totransmit the UE-specific RS is one (antenna port 7) or two (antenna port7 and antenna port 8). For example, in the base station apparatus 3 andthe RRH 4, in a case where the number of antenna ports used to transmitUE-specific RSs is two, the UE-specific RSs are multiplexed and mappedby using a code having a length of two, with two downlink resourceelements in the time domain (OFDM symbols) contiguous in the samefrequency domain (subcarrier) being one unit (the unit of CDM). In otherwords, in this case, CDM is applied to multiplexing of the UE-specificRSs. In FIG. 11, the UE-specific RSs for the antenna port 7 and theantenna port 8 are multiplexed with D1 by using CDM.

FIG. 12 is a diagram illustrating an example of mapping of downlinkreference signals in a downlink subframe in the communication system 1according to the embodiment of the present invention. Among the shadeddownlink resource elements, D1 and D2 represent UE-specific RSs. FIG. 12illustrates an example of mapping of UE-specific RSs in a case where thenumber of antenna ports used to transmit UE-specific RSs is three(antenna port 7, antenna port 8, and antenna port 9) or four (antennaport 7, antenna port 8, antenna port 9, and antenna port 10). Forexample, in the base station apparatus 3 and the RRH 4, in a case wherethe number of antenna ports used to transmit UE-specific RSs is four,the number of downlink resource elements to which the UE-specific RSsare mapped is doubled, and the UE-specific RSs are multiplexed with andmapped to downlink resource elements that differ every two antennaports. In other words, in this case, CDM and FDM (Frequency DivisionMultiplexing) are applied to multiplexing of the UE-specific RSs. InFIG. 12, the UE-specific RSs for the antenna port 7 and the antenna port8 are multiplexed with D1 by using CDM, and the UE-specific RSs for theantenna port 8 and the antenna port 9 are multiplexed with D2 by usingCDM.

For example, in a case where the number of antenna ports used totransmit UE-specific RSs in the base station apparatus 3 and the RRH 4is eight, the number of downlink resource elements to which theUE-specific RSs are mapped is doubled, and the UE-specific RSs aremultiplexed and mapped using a code having a length of four, with fourdownlink resource elements being one unit. In other words, in this case,CDM of different code lengths is applied to multiplexing of theUE-specific RSs.

In the UE-specific RS, a scramble code is further superposed on the codeof each antenna port. The scramble code is generated on the basis of acell ID and scramble ID reported from the base station apparatus 3 andthe RRH 4. For example, the scramble code is generated from apseudo-random sequence that is generated on the basis of a cell ID andscramble ID reported from the base station apparatus 3 and the RRH 4.For example, the scramble ID is a value representing 0 or 1. Thescramble ID and antenna port to be used may be subjected to jointcoding, and information representing them may be indexed. To generate ascramble code used for a UE-specific RS, parameters individuallyreported for the individual mobile station apparatuses 5 may be used.The UE-specific RS is mapped within a DL PRB pair of the PDSCH and thesecond PDCCH assigned to the mobile station apparatus 5 for which use ofthe UE-specific RS has been set.

Each of the base station apparatus 3 and the RRH 4 may assign a signalof CRS to different downlink resource elements, or may assign a signalof CRS to the same downlink resource element. For example, in a casewhere a cell ID reported from the base station apparatus 3 is differentfrom a cell ID reported from the RRH 4, a signal of CRS may be assignedto different downlink resource elements. In another example, only thebase station apparatus 3 may assign a signal of CRS to some of downlinkresource elements, whereas the RRH 4 does not have to assign a signal ofCRS to any downlink resource element. For example, in a case where acell ID is reported from only the base station apparatus 3, only thebase station apparatus 3 may assign a signal of CRS to some of downlinkresource elements, whereas the RRH 4 does not have to assign a signal ofCRS to any downlink resource element, as described above. In anotherexample, the base station apparatus 3 and the RRH 4 may assign a signalof CRS to the same downlink resource element, and the same sequence maybe transmitted from the base station apparatus 3 and the RRH 4. Forexample, in a case where the cell IDs reported from the base stationapparatus 3 and the RRH 4 are the same, a signal of CRS may be assignedin the manner described above.

FIG. 13 is a diagram illustrating a DL PRB pair to which CSI-RSs(channel state information reference signals) for eight antenna portsare mapped. FIG. 13 illustrates a case where CSI-RSs are mapped in acase where the number of antenna ports (the number of CSI ports) used inthe base station apparatus 3 and the RRH 4 is eight. In FIG. 13,illustration of a CRS, a UE-specific RS, a PDCCH, a PDCCH, and so forthis omitted to simplify the description.

The CSI-RSs are code-division-multiplexed for every two CSI ports, thatis, in individual CDM groups, two chips of orthogonal codes (Walshcodes) are used, and CSI ports (ports of CSI-RSs (antenna ports,resource grid)) are assigned to the individual orthogonal codes.Further, the individual CDM groups are frequency-division-multiplexed.By using four CDM groups, CSI-RSs for eight antenna ports, CSI ports 1to 8 (antenna ports 15 to 22), are mapped. For example, in a CDM groupC1 of the CSI-RSs, the CSI-RSs for the CSI ports 1 and 2 (antenna ports15 and 16) are code-division-multiplexed and mapped. In a CDM group C2of the CSI-RSs, the CSI-RSs for the CSI ports 3 and 4 (antenna ports 17and 18) are code-division-multiplexed and mapped. In a CDM group C3 ofthe CSI-RSs, the CSI-RSs for the CSI ports 5 and 6 (antenna ports 19 and20) are code-division-multiplexed and mapped. In a CDM group C4 of theCSI-RSs, the CSI-RSs for the CSI ports 7 and 8 (antenna ports 21 and 22)are code-division-multiplexed and mapped.

In a case where the number of antenna ports for the CSI-RSs of the basestation apparatus 3 and the RRH 4 is eight, the base station apparatus 3and the RRH 4 are capable of setting the number of layers (rank, spatialmultiplexing number) to be applied to the PDSCH to eight at maximum.Further, the base station apparatus 3 and the RRH 4 are capable oftransmitting a CSI-RS in a case where the number of antenna ports forthe CSI-RS is one, two, or four. The base station apparatus 3 and theRRH 4 are capable of transmitting a CSI-RS for one antenna port or twoantenna ports by using the CDM group 01 of the CSI-RS illustrated inFIG. 13. The base station apparatus 3 and the RRH 4 are capable oftransmitting CSI-RSs for four antenna ports by using the CDM groups 01and C2 of the CSI-RSs illustrated in FIG. 13.

The base station apparatus 3 and the RRH 4 may assign a signal of CSI-RSto different downlink resource elements, or may assign a signal ofCSI-RS to the same downlink resource element. For example, the basestation apparatus 3 and the RRH 4 may assign different downlink resourceelements and/or different signal sequences to a CSI-RS. In the mobilestation apparatus 5, a CSI-RS transmitted from the base stationapparatus 3 and a CSI-RS transmitted from the RRH 4 are identified asCSI-RSs corresponding to different antenna ports. For example, the basestation apparatus and the RRH 4 may assign the same downlink resourceelement to a CSI-RS, and the same sequence may be transmitted from thebase station apparatus 3 and the RRH 4.

The configuration of a CSI-RS (CSI-RS-Config-r10) is reported from thebase station apparatus 3 or the RRH 4 to the mobile station apparatus 5.The configuration of a CSI-RS includes at least information representingthe number of antenna ports set for CSI-RSs (antennaPortsCount-r10),information representing a downlink subframe to which a CSI-RS is mapped(subframeConfig-r10), and information representing the frequency domainto which a CSI-RS is mapped (ResourceConfig-r10). The number of antennaports for CSI-RSs is, for example, any one of one, two, four, and eight.As information representing the frequency domain in which a CSI-RS ismapped, an index indicating the position of a head resource elementamong resource elements to which the CSI-RS corresponding to the antennaport 15 (CSI port 1) is mapped is used. If the position of the CSI-RScorresponding to the antenna port 15 is determined, the CSI-RSscorresponding to the other antenna ports are uniquely determined on thebasis of a predetermined rule. As information representing a downlinksubframe to which a CSI-RS is mapped, the position and period of thedownlink subframe to which the CSI-RS is mapped are indicated by anindex. For example, if the index of subframeConfig-r10 is 5, it meansthat a CSI-RS is mapped every ten subframes, and that, in a radio framein which ten subframes serve as a unit, a CSI-RS is mapped to subframe 0(the number of a subframe in a radio frame). In another example, if theindex of subframeConfig-r10 is 1, it means that a CSI-RS is mapped everyfive subframes, and that, in a radio frame in which ten subframes serveas a unit, CSI-RSs are mapped to subframes 1 and 6.

<Configuration of Uplink Time Frame>

FIG. 14 is a diagram schematically illustrating the configuration of anuplink time frame from the mobile station apparatus 5 to the basestation apparatus 3 or the RRH 4 according to the embodiment of thepresent invention. In FIG. 14, the horizontal axis represents the timedomain and the vertical axis represents the frequency domain. An uplinktime frame is made up of a pair of physical resource blocks (referred toas an uplink physical resource block pair (UL PRB pair)). Each PRB pairis a unit of assignment of resources, and each RB has a frequency bandand a time band of predetermined widths in the uplink. One UL PRB pairis made up of two uplink PRBs that are contiguous in the time domain inthe uplink (referred to as uplink physical resource blocks (UL PRBs)).

In FIG. 14, one UL PRB is made up of twelve subcarriers in the frequencydomain of the uplink (referred to as uplink subcarriers), and is made upof seven SC-FDMA (Single-Carrier Frequency Division Multiple Access)symbols in the time domain. The system band of the uplink (referred toas an uplink system band) is an uplink communication band of the basestation apparatus 3 and the RRH 4. For example, the system bandwidth ofthe uplink (referred to as an uplink system bandwidth) has a frequencybandwidth of 20 MHz.

In the uplink system band, a plurality of UL PRB pairs are mapped on thebasis of the uplink system bandwidth. For example, the uplink systemband having a frequency bandwidth of 20 MHz is made up of one hundredand ten UL PRBs. In the time domain illustrated in FIG. 14, there are aslot made up of seven SC-FDMA symbols (referred to as an uplink slot)and a subframe made up of two uplink slots (referred to as an uplinksubframe). A unit made up of one uplink subcarrier and one SC-FDMAsymbol is referred to as a resource element (referred to as an uplinkresource element).

In each uplink subframe, at least a PUSCH used to transmit informationdata, a PUCCH used to transmit uplink control information (UCI), and aUL RS (DM RS) for demodulating the PUSCH and PUCCH (estimating channelvariations) are mapped. Although not illustrated, a PRACH used toestablish uplink synchronization is mapped to any uplink subframe.Further, although not illustrated, a UL RS (SRS) used to measure channelquality or an out-of-synchronization state is mapped to any uplinksubframe. The PUCCH is used to transmit a UCI (ACK/NACK) representing apositive acknowledgement (ACK) or a negative acknowledgement (NACK) fordata received using the PDSCH, a UCI (SR: Scheduling Request) at leastrepresenting whether or not assignment of uplink resources is to berequested, and a UCI (CQI: Channel Quality Indicator) representingreception quality in the downlink (also referred to as channel quality).

In a case where the mobile station apparatus 5 requests assignment ofuplink resources to the base station apparatus 3, the mobile stationapparatus 5 transmits a signal on the PUCCH for transmitting an SR. Thebase station apparatus 3 determines, from a result indicating that asignal has been detected in the resource of the PUCCH for transmittingan SR, that the mobile station apparatus 5 requests assignment of uplinkresources. In a case where the mobile station apparatus 5 does notrequest assignment of uplink resources to the base station apparatus 3,the mobile station apparatus 5 does not transmit any signal on thepre-assigned resource of the PUCCH for transmitting an SR. The basestation apparatus 3 determines, from a result indicating that a signalis not detected in the resource of the PUCCH for transmitting an SR,that the mobile station apparatus 5 does not request assignment ofuplink resources.

The PUCCH uses different types of signal configurations in individualcases where a UCI made up of an ACK/NACK is transmitted, where a UCImade up of an SR is transmitted, and where a UCI made up of a CQI istransmitted. The PUCCH used to transmit an ACK/NACK is referred to asPUCCH format 1a or PUCCH format 1b. In PUCCH format 1a, BPSK (BinaryPhase Shift Keying) is used as a modulation scheme for modulatinginformation regarding an ACK/NACK. In PUCCH format 1a, one-bitinformation is indicated by a modulated signal. In PUCCH format 1b, QPSK(Quadrature Phase Shift Keying) is used as a modulation scheme formodulating information regarding an ACK/NACK. In PUCCH format 1b,two-bit information is indicated by a modulated signal. The PUCCH usedto transmit an SR is referred to as PUCCH format 1. The PUCCH used totransmit a CQI is referred to as PUCCH format 2. The PUCCH used tosimultaneously transmit a CQI and an ACK/NACK is referred to as PUCCHformat 2a or PUCCH format 2b. In PUCCH format 2a or PUCCH format 2b, areference signal on an uplink pilot channel (DM RS) is multiplied by amodulated signal generated from information on an ACK/NACK. In PUCCHformat 2a, one-bit information regarding an ACK/NACK and informationregarding a CQI are transmitted. In PUCCH format 2b, two-bit informationregarding an ACK/NACK and information regarding a CQI are transmitted.

One PUSCH is made up of one or more UL PRB pairs. One PUCCH is made upof two UL PRBs that are in a symmetrical relationship in the frequencydomain within the uplink system band, and are positioned in differentuplink slots. One PRACH is made up of six UL PRB pairs. For example,referring to FIG. 14, in an uplink subframe, the UL PRB of the lowestfrequency in the first uplink slot and the UL PRB of the highestfrequency in the second uplink slot constitute one UL PRB pair used forPUCCH. In a case where the mobile station apparatus 5 is set so as notto perform simultaneous transmission of the PUSCH and PUCCH, if theresource of the PUCCH and the resource of the PUSCH are assigned in thesame uplink subframe, the mobile station apparatus 5 transmits a signalusing only the resource of the PUSCH. In a case where the mobile stationapparatus 5 is set so as to perform simultaneous transmission of thePUSCH and PUCCH, if the resource of the PUCCH and the resource of thePUSCH are assigned in the same uplink subframe, the mobile stationapparatus 5 is basically capable of transmitting a signal using both theresource of the PUCCH and the resource of the PUSCH.

A UL RS is a signal used for an uplink pilot channel. The UL RS is madeup of a demodulation reference signal (DM RS) used to estimate channelvariations of the PUSCH and PUCCH, and a sounding reference signal (SRS)used to measure channel quality for frequency scheduling and adaptivemodulation of the PUSCH of the base station apparatus 3 and the RRH 4,and to measure an out-of-synchronization state between the base stationapparatus 3 or the RRH 4 and the mobile station apparatus 5. To simplifythe description, an SRS is not illustrated in FIG. 14. A DM RS is mappedto different SC-FDMA symbols in the case of being mapped within the sameUL PRB as the PUSCH and the case of being mapped within the same UL PRBas the PUCCH. The DM RS is a signal known in the communication system 1and is used to estimate channel variations of the PUSCH and PUCCH.

In the case of being mapped within the same UL PRB as the PUSCH, the DMRS is mapped to the fourth SC-FDMA symbol in an uplink slot. In the caseof being mapped within the same UL PRB as the PUCCH including anACK/NACK, the DM RS is mapped to the third, fourth, and fifth SC-FDMAsymbols in an uplink slot. In the case of being mapped within the sameUL PRB as the PUCCH including an SR, the DM RS is mapped to the third,fourth, and fifth SC-FDMA symbols in an uplink slot. In the case ofbeing mapped within the same UL PRB as the PUCCH including a CQI, the DMRS is mapped to the second and sixth SC-FDMA symbols in an uplink slot.

An SRS is mapped within the UL PRB determined by the base stationapparatus 3, and is mapped to the fourteenth SC-FDMA symbol in an uplinksubframe (the seventh SC-FDMA symbol in the second uplink slot in theuplink subframe). The SRS can be mapped to only the uplink subframe ofthe period determined by the base station apparatus 3 in the cell(referred to as a sounding reference signal subframe; SRS subframe). Thebase station apparatus 3 assigns, for each mobile station apparatus 5, aperiod of transmitting an SRS and an UL PRB assigned to the SRS for theSRS subframe.

FIG. 14 illustrates a state where the PUCCH is mapped to the endmost ULPRB in the frequency domain in the uplink system band. Alternatively,the second or third UL PRB from the end of the uplink system band may beused for the PUCCH.

In the PUCCH, code multiplexing in the frequency domain and codemultiplexing in the time domain are used. Code multiplexing in thefrequency domain is implemented by multiplying, in units of subcarriers,each code of a code sequence by a modulated signal modulated from uplinkcontrol information. Code multiplexing in the time domain is implementedby multiplying, in units of SC-FDMA symbols, each code of a codesequence by a modulated signal modulated from uplink controlinformation. A plurality of PUCCHs are mapped to the same UL PRB,different codes are assigned to the individual PUCCHs, and codemultiplexing is realized by the assigned codes in the frequency domainor the time domain. In the PUCCH used to transmit an ACK/NACK (referredto as PUCCH format 1a or PUCCH format 1b), code multiplexing in thefrequency domain and the time domain is used. In the PUCCH used totransmit an SR (referred to as PUCCH format 1), code multiplexing in thefrequency domain and the time domain is used. In the PUCCH used totransmit a CQI (referred to as PUCCH format 2, PUCCH format 2a, or PUCCHformat 2b), code multiplexing in the frequency domain is used. Tosimplify the description, a description of code multiplexing of thePUCCH is omitted as appropriate.

The resource of the PUSCH is mapped in the time domain in the uplinksubframe after a certain number (for example, four) from the downlinksubframe in which the resource of the PDCCH including an uplink grantused to assign the resource of the PUSCH is mapped.

The resource of the PDSCH is mapped in the time domain in the samedownlink subframe as the downlink subframe in which the resource of thePDCCH including a downlink assignment used to assign the resource of thePDSCH is mapped.

<Configuration of First PDCCH>

The first PDCCH is made up of a plurality of control channel elements(CCEs). The number of CCEs used in each downlink system band depends ona downlink system bandwidth, the number of OFDM symbols constituting thefirst PDCCH, and the number of downlink reference signals on a downlinkpilot channel corresponding to the number of transmit antennas of thebase station apparatus 3 (or the RRH 4) used for communication. A CCE ismade up of a plurality of downlink resource elements, as describedbelow.

FIG. 15 is a diagram illustrating a logical relationship between thefirst PDCCH and CCEs in the communication system 1 according to theembodiment of the present invention. CCEs used between the base stationapparatus 3 (or the RRH 4) and the mobile station apparatus 5 havenumbers identifying the CCEs. The numbers are assigned to the CCEs onthe basis of a predetermined rule. Here, “CCE t” represents a CCE havinga CCE number “t”. The first PDCCH is made up of an aggregation of aplurality of CCEs (CCE Aggregation). The number of CCEs constituting theaggregation is hereinafter referred to as “CCE aggregation number”. TheCCE aggregation number constituting the first PDCCH is set by the basestation apparatus 3 on the basis of a coding rate set to the first PDCCHand the number of bits of DCI included in the first PDCCH. Anaggregation made up of n CCEs is hereinafter referred to as “CCEaggregation n”.

For example, the base station apparatus 3 configures the first PDCCHusing one CCE (CCE aggregation 1), configures the first PDCCH using twoCCEs (CCE aggregation 2), configures the first PDCCH using four CCEs(CCE aggregation 4), or configures the first PDCCH using eight CCEs (CCEaggregation 8). For example, the base station apparatus 3 uses, for themobile station apparatus 3 with good channel quality, a CCE aggregationnumber in which the number of CCEs constituting the first PDCCH issmall, and uses, for the mobile station apparatus 3 with bad channelquality, a CCE aggregation number in which the number of CCEsconstituting the first PDCCH is large. Also, for example, in the case oftransmitting DCI of a small number of bits, the base station apparatus 3uses a CCE aggregation number in which the number of CCEs constitutingthe first PDCCH is small. In the case of transmitting DCI of a largenumber of bits, the base station apparatus 3 uses a CCE aggregationnumber in which the number of CCEs constituting the first PDCCH islarge.

In FIG. 15, shaded elements are first PDCCH candidates. The first PDCCHcandidates are targets for which the mobile station apparatus 5 performsdecoding and detection of the first PDCCH. First PDCCH candidates areindependently configured for individual CCE aggregation numbers. Each ofthe first PDCCH candidates configured for the individual CCE aggregationnumbers is made up of one or more different CCEs. For each CCEaggregation number, the number of first PDCCH candidates isindependently set. The first PDCCH candidates configured for each CCEaggregation number are made up of CCEs having consecutive numbers. Themobile station apparatus 5 performs decoding and detection of the firstPDCCH for the first PDCCH candidates, the number of which is set foreach CCE aggregation number. If the mobile station apparatus 5determines that a first PDCCH for the mobile station apparatus 5 hasbeen detected, the mobile station apparatus 5 does not have to perform(may stop) decoding and detection of the first PDCCH for some of thefirst PDCCH candidates.

A plurality of downlink resource elements constituting a CCE are made upof a plurality of resource element groups (REGs, also referred to asmini-CCEs). A resource element group is made up of a plurality ofdownlink resource elements. For example, one resource element group ismade up of four downlink resource elements. FIG. 16 is a diagramillustrating an example of arrangement of resource element groups in adownlink radio frame in the communication system 1 according to theembodiment of the present invention. Here, resource element groups usedfor the first PDCCH are illustrated, and illustration and descriptionregarding a non-related part (PDSCH, second PDCCH, UE-specific RS,CSI-RS) are omitted. Here, a description will be given of a case wherethe first PDCCH is made up of the first to third OFDM symbols anddownlink reference signals (R0, R1) corresponding to the CRSs for twotransmit antennas (antenna port 0, antenna port 1) are mapped. In FIG.16, the vertical axis represents the frequency domain and the horizontalaxis represents the time domain.

In the example of arrangement illustrated in FIG. 16, one resourceelement group is made up of four downlink resource elements that areadjacent in the frequency domain. In FIG. 16, the downlink resourceelements with the same number of the first PDCCH belong to the sameresource element group. Resource element groups are formed, withresource elements R0 (a downlink reference signal for the antenna port0) and R1 (a downlink reference signal for the antenna port 1) to whichdownlink reference signals are mapped being skipped. In FIG. 16, anumber “1” is assigned to the resource element group of the first OFDMsymbol with the lowest frequency, a number “2” is assigned to theresource element group of the second OFDM symbol with the lowestfrequency, and a number “3” is assigned to the resource element group ofthe third OFDM symbol with the lowest frequency. Also, FIG. 16illustrates that a number “4” is assigned to the resource element groupadjacent in frequency to the resource element group having a number “2”of the second OFDM symbol to which a downlink reference signal is notmapped, and that a number “5” is assigned to the resource element groupadjacent in frequency to the resource element group having a number “3”of the third OFDM symbol to which a downlink reference signal is notmapped. Further, FIG. 16 illustrates that a number “6” is assigned tothe resource element group adjacent in frequency to the resource elementgroup having a number “1” of the first OFDM symbol, that a number “7” isassigned to the resource element group adjacent in frequency to theresource element group having a number “4” of the second OFDM symbol,and that a number “8” is assigned to the resource element group adjacentin frequency to the resource element group having a number “5” of thethird OFDM symbol.

A CCE is made up of a plurality of resource element groups illustratedin FIG. 16. For example, one CCE is made up of nine different resourceelement groups distributed in the frequency domain and the time domain.Specifically, regarding a CCE used for the first PDCCH, interleave isperformed on all the resource element groups having numbers illustratedin FIG. 16 in units of resource element groups by using a blockinterleaver for the entire downlink system band, and nine resourceelement groups having consecutive numbers obtained through interleaveconstitute one CCE.

<Configuration of Second PDCCH>

FIG. 17 is a diagram schematically illustrating an example of theconfiguration of regions where a second PDCCH is possibly mapped in thecommunication system 1 according to the embodiment of the presentinvention (hereinafter referred to as second PDCCH regions to simplifythe description). The base station apparatus 3 is capable of forming(configuring, mapping) a plurality of second PDCCH regions (second PDCCHregion 1, second PDCCH region 2, and second PDCCH region 3) in adownlink system band. One second PDCCH region is made up of one or moreDL PRB pairs. In a case where one second PDCCH region is made up of aplurality of DL PRB pairs, the second PDCCH region may be made up of DLPRB pairs that are distributed in the frequency domain or DL PRB pairsthat are contiguous in the frequency domain. For example, the basestation apparatus 3 is capable of configuring a second PDCCH region foreach of a plurality of mobile station apparatuses 5.

For the individual second PDCCH regions, different transmission methodsare set for signals to be mapped thereto. For example, precodingprocessing is applied to a signal mapped to a certain second PDCCHregion. For example, precoding processing is not applied to a signalmapped to a certain second PDCCH region. In the second PDCCH region inwhich precoding processing is applied to a mapped signal, the sameprecoding processing can be applied to a second PDCCH and a UE-specificRS in a DL PRB pair. In the second PDCCH region in which precodingprocessing is applied to a mapped signal, different types of precodingprocessing (applied precoding vectors are different) (applied precodingmatrices are different) may be applied to a second PDCCH and aUE-specific RS between different DL PRB pairs.

One second PDCCH is made up of one or more E-CCEs (first elements). FIG.18 is a diagram illustrating a logical relationship between a secondPDCCH and E-CCEs in the communication system 1 according to theembodiment of the present invention. E-CCEs used between the basestation apparatus 3 (or the RRH 4) and the mobile station apparatus 5have numbers identifying the E-CCEs. Numbering of the E-CCEs isperformed on the basis of a predetermined rule. Here, “E-CCE t”represents an E-CCE having an E-CCE number (E-CCE index) “t”. The secondPDCCH is made up of an aggregation including a plurality of E-CCEs(E-CCE Aggregation). The number of E-CCEs included in the aggregation ishereinafter referred to as “E-CCE aggregation number”. For example, anE-CCE aggregation number constituting the second PDCCH is set by thebase station apparatus 3 on the basis of a coding rate set to the secondPDCCH and the number of bits of DCI included in the second PDCCH. Anaggregation made up of n E-CCEs is hereafter referred to as “E-CCEaggregation n”.

For example, the base station apparatus 3 configures a second PDCCHusing one E-CCE (E-CCE aggregation 1), configures a second PDCCH usingtwo E-CCEs (E-CCE aggregation 2), configures a second PDCCH using fourE-CCEs (E-CCE aggregation 4), and configures a second PDCCH using eightE-CCEs (E-CCE aggregation 8). For example, the base station apparatus 3uses, for the mobile station apparatus 3 with good channel quality, anE-CCE aggregation number in which the number of E-CCEs constituting thesecond PDCCH is small, and uses, for the mobile station apparatus 3 withbad channel quality, an E-CCE aggregation number in which the number ofE-CCEs constituting the second PDCCH is large. For example, in the caseof transmitting DCI of a small number of bits, the base stationapparatus 3 uses an E-CCE aggregation number in which the number ofE-CCEs constituting the second PDCCH is small, and in the case oftransmitting DCI of a large number of bits, the base station apparatus 3uses an E-CCE aggregation number in which the number of E-CCEsconstituting the second PDCCH is large.

In FIG. 18, shaded elements are second PDCCH candidates. The secondPDCCH candidates (E-PDCCH candidates) are targets on which the mobilestation apparatus 5 performs decoding and detection of a second PDCCH.Second PDCCH candidates are independently configured for individualE-CCE aggregation numbers. Each of the second PDCCH candidatesconfigured for individual E-CCE aggregation numbers is made up of one ormore different E-CCEs. The number of second PDCCH candidates isindependently set for each E-CCE aggregation number. The second PDCCHcandidates configured for each E-CCE aggregation number are made up ofE-CCEs having consecutive numbers or inconsecutive numbers. The mobilestation apparatus 5 performs decoding and detection of a second PDCCH onthe second PDCCH candidates the number of which is set for each E-CCEaggregation number. In a case where the mobile station apparatus 5determines that a second PDCCH for the mobile station apparatus 5 hasbeen detected, the mobile station apparatus 5 does not have to perform(may stop) decoding and detection of a second PDCCH on some of theconfigured second PDCCH candidates.

The number of E-CCEs configured in a second PDCCH region depends on thenumber of DL PRB pairs constituting the second PDCCH region. Forexample, the amount of resources (the number of resource elements)corresponding to one E-CCE is substantially equal to a quarter ofresources that can be used for a signal on a second PDCCH within one DLPRB pair (except resource elements used for a downlink reference signaland a first PDCCH). One second PDCCH region may be made up of only oneslot of a downlink subframe, and may be made up of a plurality of PRBs.Alternatively, the second PDCCH region may be independently made up ofthe first slot and the second slot in a downlink subframe. In theembodiment of the present invention, a description will be mainly givenof a case where a second PDCCH region is made up of a plurality of DLPRB pairs in a downlink subframe for simplifying the description, butthe present invention is not limited to such a case.

FIG. 19 is a diagram illustrating an example of the configuration ofregions (resources) according to the embodiment of the presentinvention. Here, the resources constituting regions are illustrated, andthe illustration and description of non-related parts (PDSCH and firstPDCCH) are omitted. Here, one DL PRB pair is illustrated. Here, adescription will be given of a case where a second PDCCH is made up ofthe fourth to fourteenth OFDM symbols of the first slot of a downlinksubframe, and where CRSs (R0, R1) for two transmit antennas (antennaport 0, antenna port 1) and a UE-specific RS (D1) for one or twotransmit antennas (antenna port 7, antenna port 8, not illustrated) aremapped. In FIG. 19, the vertical axis represents the frequency domainand the horizontal axis represents the time domain. A quarter ofresources that can be used for a second PDCCH in a DL PRB pair isconfigured as one region. For example, a quarter of resources of a DLPRB pair in the frequency domain is configured as one region.Specifically, a resource corresponding to three subcarriers in a DL PRBpair is configured as one region. For example, the E-CCEs in the DL PRBpair are given numbers in ascending order from the E-CCE including a lowsubcarrier in the frequency domain.

FIG. 20 is a diagram illustrating an example of the configuration ofregions according to the embodiment of the present invention. Comparedto the example illustrated in FIG. 19, the number of antenna ports forUE-specific RSs is different. FIG. 20 illustrates a case whereUE-specific RSs (D1, D2) for three or four transmit antennas (antennaport 7, antenna port 8, antenna port 9, antenna port 10, notillustrated) are mapped.

Different types of physical resource mapping (first physical resourcemapping, second physical resource mapping) are applied to second PDCCHregions. Specifically, the configuration of E-CCEs constituting onesecond PDCCH (aggregation method) differs. For example, a second PDCCHto which the first physical resource mapping is applied is referred toas “Localized E-PDCCH”. For example, a second PDCCH to which the secondphysical resource mapping is applied is referred to as “DistributedE-PDCCH”. For example, the Localized E-PDCCH is made up of one E-CCE(E-CCE aggregation 1), or is made up of two E-CCEs (E-CCE aggregation2), or is made up of four E-CCEs (E-CCE aggregation 4). The LocalizedE-PDCCH in which the E-CCE aggregation number is 2 or more is made up ofa plurality of E-CCEs having consecutive E-CCE numbers (consecutive inthe frequency domain). For example, the Distributed E-PDCCH is made upof four E-CCEs (E-CCE aggregation 4) or is made up of eight E-CCEs(E-CCE aggregation 8). The Distributed E-PDCCH is made up of a pluralityof E-CCEs associated with noncontiguous regions in the frequency domain.For example, the four E-CCEs constituting the Distributed E-PDCCH ofE-CCE aggregation 4 are made up of regions in different DL PRB pairs.The eight E-CCEs constituting the Distributed E-PDCCH of E-CCEaggregation 8 may be made up of regions in different DL PRB pairs, andsome of the plurality of E-CCEs may be made up of regions in the same DLPRB pair. For example, a plurality of E-CCEs that are used for oneLocalized E-PDCCH are made up of regions in one DL PRB pair, and aplurality of E-CCEs that are used for one Distributed E-PDCCH are madeup of regions in a plurality of DL PRB pairs.

FIG. 21 is a diagram illustrating an example of the configuration ofE-CCEs and Localized E-PDCCHs. FIG. 21 illustrates a case where a secondPDCCH is made up of the fourth to fourteenth OFDM symbols of a downlinksubframe. In FIG. 21, the vertical axis represents the frequency domain,and the horizontal axis represents the time domain. For example, acertain E-CCE is made up of two E-CCEs having a small number (low in thefrequency domain) among the regions (resources) in a certain DL PRB pair(for example, an E-CCE 2151 is made up of regions 2101 and 2102, inother words, the E-CCE 2151 is associated with the regions 2101 and2102). Also, a certain E-CCE is made up of two E-CCEs having a largenumber (high in the frequency domain) among the regions in a certain DLPRB pair (for example, an E-CCE 2152 is made up of regions 2103 and2104).

FIG. 22 is a diagram illustrating an example of the configuration ofE-CCEs and Distributed E-PDCCHs. FIG. 22 illustrates a case where asecond PDCCH is made up of the fourth to fourteenth OFDM symbols of adownlink subframe. In FIG. 22, the vertical axis represents thefrequency domain, and the horizontal axis represents the time domain.For example, in a certain E-CCE, two regions are made up of regions indifferent DL PRB pairs. For example, a certain E-CCE is made up ofE-CCEs having the smallest number (lowest in the frequency domain) amongthe regions in individual DL PRB pairs (for example, an E-CCE 2251 ismade up of regions 2201 and 2205, in other words, the E-CCE 2251 isassociated with the regions 2201 and 2205). For example, a certain E-CCEis made up of regions having the second smallest number (second lowestin the frequency domain) among the regions in individual DL PRB pairs(for example, an E-CCE 2252 is made up of regions 2202 and 2206). Forexample, a certain E-CCE is made up of regions having the third smallestnumber (third lowest in the frequency domain) among the regions inindividual DL PRB pairs (for example, an E-CCE 2253 is made up ofregions 2203 and 2207). For example, a certain E-CCE is made up ofregions having the largest number (highest in the frequency domain)among the regions in individual DL PRB pairs (for example, an E-CCE 2254is made up of regions 2204 and 2208).

FIG. 23 is a diagram illustrating an example of the configuration ofE-CCEs and Localized E-PDCCHs. FIG. 23 illustrates a case where a secondPDCCH is made up of the fourth to fourteenth OFDM symbols of a downlinksubframe. In FIG. 23, the vertical axis represents the frequency domain,and the horizontal axis represents the time domain. For example, acertain E-CCE is made up of one region in a certain DL PRB pair (forexample, an E-CCE 2351 is made up of a region 2301, in other words, theE-CCE 2351 is associated with the region 2301). Another certain E-CCE ismade up of a certain region in a certain DL PRB pair (for example, anE-CCE 2152 is made up of regions 2103 and 2104, in other words, theE-CCE 2152 is associated with the regions 2103 and 2104). In this way, acertain E-CCE may be made up of (or associated with) one region asillustrated in FIG. 23, unlike in FIGS. 21 and 22, in which a certainE-CCE is made up of (or associated with) two regions. FIG. 23illustrates an example of the configuration of Localized E-PDCCHs. Inthe configuration of Distributed E-PDCCHs, an E-CCE may be made up of(or associated with) one region. Although not illustrated, a certainE-CCE may be made up of (or associated with) three or more regions. Thenumber of regions included in an E-CCE (that is, the correspondencebetween an E-CCE and regions) may be reported from the base stationapparatus 3, and configuration may be performed accordingly in themobile station apparatus 5. For example, the information may be reportedusing RRC (Radio Resource Control) signaling. The report may beperformed for each mobile station apparatus 5, or may be associated withother information. For example, the report may be associated with thevalue of CFI (Control Format Indicator), which is the number of OFDMsymbols of a first PDCCH included in DL PRB pairs, a DCI Format, thenumber of ports of CRS, or the like. Alternatively, a possible set ofE-CCE aggregation number may be explicitly signaled from a base stationto a terminal (for example, RRC signaling). For example, in the case ofbeing associated with the value of CFI, two regions may constitute (ormay be associated with) one E-CCE as illustrated in FIGS. 21 and 22 ifthe value of CFI is 2 or 3, and one region may constitute (or may beassociated with) one E-CCE as illustrated in FIG. 23 if the value of CFIis 0. In another example, in the case of DCI Formats 2, 2A, 2B, and 2C(for example, when a system bandwidth is 10 MHz, these are formatshaving a bit number of 56 bits or more. From another point of view,these are formats used for MIMO transmission, and two MCS (Modulationand Coding Scheme) values corresponding to two codewords can bereported. Also, a DCI Format 4 including two MCSs may be included), tworegions may constitute one E-CCE as illustrated in FIGS. 21 and 22. Inthe case of DCI Formats 0, 1A, 1C, 3, and 3A (for example, when a systembandwidth is 10 MHz, these are formats having a bit number of 44 bits orless. From another point of view, these are formats used forsingle-antenna transmission or transmission diversity, and one MCS(Modulation and Coding Scheme) value corresponding to one codeword canbe reported), one region may constitute one E-CCE as illustrated in FIG.23. In another example, two regions may constitute one E-CCE asillustrated in FIGS. 21 and 22 in a case where two or more ports (forexample, antenna ports 0 and 1 or antenna ports 0, 1, 2, and 3) areconfigured for a CRS, and one region may constitute one E-CCE asillustrated in FIG. 23 in a case where one port or less (for example,only an antenna port 0) is configured for a CRS. In a case where thecorrespondence between a region and an E-CCE is set in association withthe above-described information (that is, CFI, the number of CRS ports,etc.), a threshold may be reported from the base station apparatus 3using RRC (Radio Resource Control) signaling. For example, in a casewhere a CFI is associated, it may be reported that CFI is 2 or more andtwo regions constitute (or are associated with) one E-CCE, or that CFIis 1 or more and two regions constitute (or are associated with) oneE-CCE. Also, it may be reported whether one region constitutes one E-CCEas illustrated in FIG. 23 in a case where one port or less (for example,only an antenna port 0) is configured for a CRS, or whether one regionconstitutes one E-CCE as illustrated in FIG. 23 in a case where a portis not configured for a CRS (CRS is not transmitted).

FIG. 24 illustrates an example in which E-CCEs are mapped to regionsfrom a viewpoint of the base station apparatus 3. Here, one E-CCE ismade up of one region as in the case of FIG. 23, but one E-CCE may bemade up of two regions as in the cases of FIGS. 21 and 22. FIG. 24 alsoillustrates an example of the configuration of Distributed E-PDCCH.First, the base station apparatus 3 notifies each mobile stationapparatus 5 of a bit map using RRC (Radio Resource Control) signaling.Here, a bit map may indicate a PRB pair to which a second PDCCH ispossibly mapped, and the number of resources of E-CCEs and the number ofresources of regions at the time of mapping of the E-CCEs and regions. Asearch space (SS) indicating an E-CCE to which a downlink controlchannel is possibly assigned, a signal generated from DCI addressed tothe mobile station apparatus 5 being mapped to the downlink controlchannel, is possibly reported separately. In accordance with thereported bit map, the base station apparatus 3 determines the number ofresources of E-CCEs (the number of resources of E-CCEs is 16 in FIG. 24.Four PRB pairs are selected by the bit map and the individual PRB pairsare associated with four E-CCEs, and thus the number of resources of theE-CCEs is 16). In the case of Distributed E-PDCCH, the E-CCEs arerearranged, and the E-CCEs (after rearrangement) are obtained.Subsequently, the E-CCEs (after rearrangement) are associated withcorresponding regions. For example, in FIG. 24, the E-CCEs (afterrearrangement) #0, #4, #8, #12, #2, #6, #10, #14, #1, #5, #9, #13, #3,#7, #11, and #15 are respectively associated with the regions #0, #1,#2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, #14, #15, and #16 inorder. Subsequently, in FIG. 24, the regions #1 to #3 are mapped to aPRB pair 2402, the regions #4 to #7 are mapped to a PRB pair 2403, theregions #8 to #11 are mapped to a PRB pair 2405, and the regions #12 to#15 are mapped to a PRB pair 2406. That is, in the example illustratedin FIG. 24, it is understood that four regions are assigned to the PRBpair 2402 through the above-described process, and the individualassigned regions are associated with the E-CCEs #0, #4, #8, and #12. Anexample of Distributed E-PDCCH is described here. In this case, the basestation apparatus 3 notifies each mobile station apparatus 5 of a commonbit map, and accordingly the plurality of mobile station apparatuses 5are capable of using common mapping for rearrangement used for E-CCEsand E-CCEs (after rearrangement). Here, one E-CCE is made up of oneregion as in the case of FIG. 23, but one E-CCE may be made up of tworegions as in the cases of FIGS. 21 and 22. In this case, there is apossibility that an E-CCE number (E-CCE index) is associated with a subE-CCE number (sub E-CCE index) (As illustrated in FIGS. 26 and 27, forexample, the E-CCE #0 is associated with sub E-CCEs #0 and #1, and theE-CCE #1 is associated with sub E-CCEs #2 and #3. Also, sub E-CCEindices are associated with regions as illustrated in FIG. 26. Forexample, a PRB pair 2602 is associated with the sub E-CCEs #0, #4, #8,and #12.) The search space may include a common search space that iscommonly configured for the plurality of mobile station apparatuses 5and a terminal-specific search space that is individually configured forthe plurality of mobile station apparatuses 5. The common search spacemay be configured, with a specific E-CCE number being a start point. Forexample, the E-CCE #0 may always be configured as a start point of acommon search space, and another specific E-CCE number may be a startpoint of the common search space. Also, the start point of aterminal-specific search space may be explicitly configured for themobile station apparatus 5 by the base station apparatus 3. For example,different start points may be configured for the individual mobilestation apparatuses 5. Accordingly, even in a case where a common bitmap is reported to the plurality of mobile station apparatuses 5, andthe mobile station apparatuses 5 receive a second PDCCH using the sameresource blocks pair, different terminal-specific search spaces can beconfigured for the individual mobile station apparatuses 5.

FIG. 25 illustrates an example in which regions are mapped to E-CCEsfrom a viewpoint of the mobile station apparatus 5. The correspondencebetween E-CCEs and regions illustrated in FIG. 25 is completely the sameas that in FIG. 24. Here, one E-CCE is made up of one region as in thecase of FIG. 23, but one E-CCE may be made up of two regions as in thecases of FIGS. 21 and 22. FIG. 25 also illustrates an example of theconfiguration of Distributed E-PDCCH. First, the mobile stationapparatus 5 is notified of, by the base station apparatus 3, a bit mapusing RRC (Radio Resource Control) signaling. Here, a bit map mayindicate a PRB pair to which a second PDCCH is possibly mapped, and thenumber of resources of E-CCEs and the number of resources of regions atthe time of mapping of the E-CCEs and regions. A search space (SS)indicating an E-CCE to which a downlink control channel is possiblyassigned, a signal generated from DCI addressed to the mobile stationapparatus 5 being mapped to the downlink control channel, is possiblyreported separately. The mobile station apparatus 3 extracts regions onthe basis of the reported bit map. In the example illustrated in FIG.24, for example, four regions are assigned to a PRB pair 2502, and theindividual assigned regions are #0, #1, #2, and 3. More specifically,the regions #0 to 15 associated with PRB pairs 2502, 2503, 2505, and2506 are extracted. Subsequently, the regions #0 to #15 are associatedwith the rearranged E-CCEs #0 to #15 on the basis of the orderillustrated in FIG. 25. After that, the rearranged E-CCEs are rearrangedto E-CCEs. In accordance with this procedure, the mobile stationapparatus 3 rearranges E-CCEs using the received signal and bit map, anddemodulates a second PDCCH. The search space includes a common searchspace (CSS) monitored (for example, demodulated) by a plurality ofmobile station apparatuses 5, and a UE specific search space (USS)monitored (for example, demodulated) by only a specific mobile stationapparatus 5. In the examples illustrated in FIGS. 24 and 25, specificE-CCE numbers (for example, E-CCE numbers #0 to 7, or a start positionof a common search space is E-CCE number #0) may be set to a commonsearch space. Separately from this, each mobile station apparatus 5 maybe notified of a UE specific search space.

FIG. 26 illustrates an example in which E-CCEs are mapped to regionsfrom a viewpoint of the base station apparatus 3. Here, an example isillustrated in which one E-CCE is made up of two regions as in the casesof FIGS. 21 and 22. FIG. 26 also illustrates an example of theconfiguration of Distributed E-PDCCH. First, the base station apparatus3 notifies each mobile station apparatus 5 of a bit map using RRC (RadioResource Control) signaling. Here, a bit map may indicate a PRB pair towhich a second PDCCH is possibly mapped, and the number of resources ofE-CCEs and the number of resources of regions at the time of mapping ofthe E-CCEs and regions. A search space (SS) indicating an E-CCE to whicha downlink control channel is possibly assigned, a signal generated fromDCI addressed to the mobile station apparatus 5 being mapped to thedownlink control channel, is possibly reported separately. In accordancewith the reported bit map, the base station apparatus 3 determines thenumber of resources of E-CCEs (the number of resources of E-CCEs is 8 inFIG. 26. Four PRB pairs are selected by the bit map and the individualPRB pairs are associated with two E-CCEs, and thus the number ofresources of the E-CCEs is 8), and these are associated with sub E-CCEs(for example, E-CCE #0 is associated with sub E-CCEs #0 and 1, and E-CCE#1 is associated with sub E-CCEs #2 and 3). The sub E-CCEs arerearranged in the case of Distributed E-PDCCH, and become sub E-CCEs(after rearrangement). Subsequently, the sub E-CCEs (afterrearrangement) are associated with corresponding regions. For example,in FIG. 26, the sub E-CCEs (after rearrangement) #0, #4, #8, #12, #2,#6, #10, #14, #1, #5, #9, #13, #3, #7, #11, and #15 are respectivelyassociated with the regions #0, #1, #2, #3, #4, #5, #6, #7, #8, #9, #10,#11, #12, #13, #14, #15, and #16 in order. Subsequently, in FIG. 26, theregions #1 to #3 are mapped to a PRB pair 2402, the regions #4 to #7 aremapped to a PRB pair 2403, the regions #8 to #11 are mapped to a PRBpair 2405, and the regions #12 to #15 are mapped to a PRB pair 2406.That is, in the example illustrated in FIG. 26, it is understood thatfour regions are assigned to the PRB pair 2402 through theabove-described process, and the individual assigned regions areassociated with the sub E-CCEs #0, #4, #8, and #12 (from anotherviewpoint, E-CCEs #0, #2, #4, and #6). An example of Distributed E-PDCCHis described here. In this case, the base station apparatus 3 notifieseach mobile station apparatus 5 of a common bit map, and accordingly theplurality of mobile station apparatuses 5 are capable of using commonmapping for rearrangement used for E-CCEs and E-CCEs (afterrearrangement). The search space includes a common search space (CSS)monitored (for example, demodulated) by a plurality of mobile stationapparatuses 5, and a UE specific search space (USS) monitored (forexample, demodulated) by only a specific mobile station apparatus 5. Inthe example illustrated in FIG. 24, specific E-CCE numbers (for example,E-CCE numbers #0 to 7, or a start position of a common search space isE-CCE number #0) may be set to a common search space. Separately fromthis, each mobile station apparatus 5 may be notified of a UE specificsearch space.

FIG. 27 illustrates an example in which regions are mapped to E-CCEsfrom a viewpoint of the mobile station apparatus 5. The correspondencebetween E-CCEs and regions illustrated in FIG. 27 is completely the sameas that in FIG. 26. Here, one E-CCE is made up of two regions as in thecases of FIGS. 21 and 22. FIG. 25 also illustrates an example of theconfiguration of Distributed E-PDCCH. First, the mobile stationapparatus 5 is notified of, by the base station apparatus 3, a bit mapusing RRC (Radio Resource Control) signaling. Here, a bit map mayindicate a PRB pair to which a second PDCCH is possibly mapped, and thenumber of resources of E-CCEs and the number of resources of regions atthe time of mapping of the E-CCEs and regions. A search space (SS)indicating an E-CCE to which a downlink control channel is possiblyassigned, a signal generated from DCI addressed to the mobile stationapparatus 5 being mapped to the downlink control channel, is possiblyreported separately. The mobile station apparatus 3 extracts regions onthe basis of the reported bit map. In the example illustrated in FIG.27, for example, four regions are assigned to a PRB pair 2702, and theindividual assigned regions are #0, #1, #2, and 3. More specifically,regions #0 to 15 associated with PRB pairs 2702, 2703, 2705, and 2706are extracted. Subsequently, the regions #0 to #15 are associated withthe rearranged sub E-CCEs #0 to #15 on the basis of the orderillustrated in FIG. 27 (for example, the region 1 is associated with thesub E-CCE #4, and the region 2 is associated with the sub E-CCE #8).After that, the rearranged sub E-CCEs are rearranged to sub E-CCEs.Further, the sub E-CCEs are coupled to the E-CCEs (for example, the subE-CCEs #0 and #1 are coupled to the E-CCE #0). In accordance with thisprocedure, the mobile station apparatus 3 rearranges E-CCEs using thereceived signal and bit map, and demodulates a second PDCCH. The searchspace includes a common search space (CSS) monitored (for example,demodulated) by a plurality of mobile station apparatuses 5, and a UEspecific search space (USS) monitored (for example, demodulated) by aspecific mobile station apparatus 5. In the examples illustrated inFIGS. 26 and 27, specific E-CCE numbers (for example, E-CCE numbers #0to 7, or a start position of a common search space is E-CCE number #0)may be set to a common search space. Separately from this, each mobilestation apparatus 5 may be notified of a UE specific search space.

FIG. 28 illustrates another example in which E-CCEs are mapped toregions. Here, one E-CCE is made up of one region as in the case of FIG.23, but one E-CCE may be made up of two regions as in the cases of FIGS.21 and 22. FIG. 28 also illustrates an example of the configuration ofDistributed E-PDCCH. First, the base station apparatus 3 notifies eachmobile station apparatus 5 of a bit map using RRC (Radio ResourceControl) signaling. Here, a bit map indicates a PRB pair to which asecond PDCCH is possibly mapped, and a search space (SS) indicating anE-CCE (or region) to which DCI addressed to the mobile station apparatus5 is possibly assigned. The number of resources of E-CCEs and the numberof resources of regions at the time of mapping of the E-CCEs and regionsare independent of the bit map, and is determined by, for example, asystem bandwidth (in FIG. 28, the system bandwidth corresponds to 6 RBs(resource blocks) and it is assumed that each PRB pair is associatedwith four E-CCEs, and 24 E-CCEs are assumed). First, the base stationapparatus 3 and the mobile station apparatus 5 set the number of E-CCEson the basis of the system bandwidth. Subsequently, the base stationapparatus 3 and the mobile station apparatus 5 rearrange the E-CCEs togenerate rearranged E-CCEs. Here, the rearranged E-CCEs are associatedwith regions. In FIG. 28, the bit map is associated with the regions,and indicates regions to which a second PDCCH including DCI addressed tothe mobile station apparatus 5 is possibly assigned. As a result ofassociating the regions indicated by the bit map with the E-CCEs (afterrearrangement), the E-CCEs included in the search space become clear(the shaded part included in the E-CCEs (after rearrangement) in FIG.28). On the other hand, there is a possibility that a second PDCCH isassigned to the corresponding regions (the shaded part included in theregions in FIG. 28). For example, in FIG. 28, four regions are assignedto a PRB pair 2802, and the individual regions are associated withE-CCEs #2, #8, #14, and #20. Likewise, PRB pairs 2803, 2805, and 2806are assigned to the mobile station apparatus 5 by the bit map, and theE-CCEs #2 to #5, #8 to #11, #14 to #17, and #20 to #23 correspond to thesearch space for the mobile station apparatus 5). In this case, the basestation apparatus 3 notifies the individual mobile station apparatuses 5of different bit maps, and thereby different search spaces can beconfigured in the plurality of mobile station apparatuses 5. Here, oneE-CCE is made up of one region as in the case of FIG. 23, but one E-CCEmay be made up of two regions as in the cases of FIGS. 21 and 22. Inthis case, an E-CCE number (E-CCE index) is possibly associated with asub E-CCE number (sub E-CCE index) (although not illustrated, forexample, the E-CCE #0 is associated with sub E-CCEs #0 and #1, and theE-CCE #1 is associated with sub E-CCEs #2 and #3. Subsequently, the subE-CCE indices are associated with regions as illustrated in FIG. 25. Forexample, the PRB pair 2502 is associated with sub E-CCEs #2, #8, #14,and #20.)

Examples in which the correspondence between E-CCEs and regions is setare illustrated in FIGS. 21, 22, and 23. Alternatively, thecorrespondence between E-CCEs and regions is always that illustrated inFIG. 23 (one E-CCE is associated with one region) or that illustrated inFIGS. 21 and 22 (one E-CCE is associated with two regions), whereas theE-CCE aggregation number constituting a second PDCCH may vary dependingon a condition. For example, the E-CCE aggregation number may beassociated with the value of CFI (Control Format Indicator), which isthe number of OFDM symbols of a first PDCCH included in a DL PRB pair,DCI Format, the number of ports of CRS, or the like. For example, in thecase of being associated with the value of CFI, two, four, eight, orsixteen E-CCEs may constitute one second PDCCH in a case where the valueof CFI is 2 or 3, and one, two, four, or eight E-CCEs may constitute onesecond PDCCH in a case where the value of CFI is 0. In another example,in the case of DCI format 2, 2A, 2B, or 2C, two, four, eight, or sixteenE-CCEs may constitute a second PDCCH, and in the case of DCI format 0,1A, 1C, 3, or 3A, one, two, four, or eight E-CCEs may constitute asecond PDCCH. In another example, in a case where two or more ports (forexample, antenna ports 0 and 1 or antenna ports 0, 1, 2, and 3) areconfigured for CRS, two, four, eight, or sixteen E-CCEs may constitute asecond PDCCH, and in a case where one port or less (for example, onlyantenna port 0) is configured for CRS, one, two, four, or eight E-CCEsmay constitute a second PDCCH. In a case where the correspondencebetween regions and E-CCEs is set in association with theabove-described information, a threshold may be reported by the basestation apparatus 3 using RRC (Radio Resource Control) signaling. Forexample, the E-CCE aggregation number constituting a second PDCCH is setby the base station apparatus 3 on the basis of the coding rate set forthe second PDCCH and a bit number of DCI included in the second PDCCH.The aggregation made up of n E-CCEs is hereinafter referred to as “E-CCEaggregation n”.

For example, the base station apparatus 3 configures a second PDCCHusing one E-CCE (E-CCE aggregation 1), configures a second PDCCH usingtwo E-CCEs (E-CCE aggregation 2), configures a second PDCCH using fourE-CCEs (E-CCE aggregation 4), configures a second PDCCH using eightE-CCEs (E-CCE aggregation 8), or configures a second PDCCH using sixteenE-CCEs (E-CCE aggregation 16). For example, the base station apparatus 3uses, for the mobile station apparatus 3 with good channel quality, anE-CCE aggregation number in which the number of E-CCEs constituting thesecond PDCCH is small, and uses, for the mobile station apparatus 3 withbad channel quality, an E-CCE aggregation number in which the number ofE-CCEs constituting the second PDCCH is large. Further, for example, thebase station apparatus 3 uses an E-CCE aggregation number in which thenumber of E-CCEs constituting the second PDCCH is small in the case oftransmitting DCI of a small bit number, and uses an E-CCE aggregationnumber in which the number of E-CCEs constituting the second PDCCH islarge in the case of transmitting DCI of a large bit number.

In another example, setting of the correspondence between E-CCEs andregions and setting of an E-CCE aggregation number constituting thesecond PDCCH may be used together. For example, in association with thevalue of CFI (Control Format Indicator), a DCI Format, the number ofports for CRS, or the like, the correspondence between E-CCEs andregions and the E-CCE aggregation number constituting the second PDCCHmay be simultaneously set, or signaling (for example, RRC signaling) maybe explicitly performed from the base station apparatus 3 to the mobilestation apparatus 5. For example, in a case where one E-CCE isassociated with one region (in the case of FIG. 23), the E-CCEaggregation number may be set to 1, 2, 4, or 8. In a case where oneE-CCE is associated with two regions (in the cases of FIGS. 21 and 22),the E-CCE aggregation number may be set to 2, 4, 8, or 16. In anotherexample, in a case where one E-CCE is associated with one region (in thecase of FIG. 23), the E-CCE aggregation number may be set to 1, 2, 4, or8. In a case where one E-CCE is associated with two regions (in thecases of FIGS. 21 and 22), the E-CCE aggregation number may be set to 2,4, 8, or 12. In this way, E-CCE aggregation numbers are not required tohave a relationship of multiples. At this time, as the number of secondPDCCH candidates (E-PDCCH candidates) represented by shaded parts inFIG. 18, the number of second PDCCH candidates is independently set foreach E-CCE aggregation number. The number of second PDCCH candidates maybe set to a different value on the basis of setting of thecorrespondence between the E-CCEs and regions or setting of the E-CCEaggregation number constituting the second PDCCH. For example, in a casewhere one E-CCE is associated with one region (in the case of FIG. 23)and where the E-CCE aggregation number is set to 1, 2, 4, or 8, thenumber of second PDCCH candidates may be set to 4 in a case where E-CCEaggregation number=2. In a case where one E-CCE is associated with tworegions (in the cases of FIGS. 21 and 22) and where the E-CCEaggregation number is set to 2, 4, 8, or 16, the number of second PDCCHcandidates may be set to 6 in a case where E-CCE aggregation number=2.In this way, as a result of performing both setting of thecorrespondence between E-CCEs and regions and setting of the E-CCEaggregation number constituting the second PDCCH, the base stationapparatus 3 is capable of controlling the quality of the second PDCCHmore flexibly. That is, even in a situation where the number of CRSports is variously set, the number of OFDM symbols can be operated whileappropriately maintaining the quality of the second PDCCH, byappropriately setting the resources to be used for the second PDCCHusing the above-described method.

Referring to FIGS. 24 to 27, in the second physical resource mapping, inthe E-CCEs constituting one Distributed E-PDCCH, the Distributed E-PDCCHmay be formed using E-CCEs whose positions in the individual DL PRBpairs (frequency positions) are different (for example, in FIG. 24, anE-PDCCH is made up of E-CCE #0 and E-CCE #1, and the leftmost region inthe PRB pair 2402 and the leftmost region in the PRB pair 2405 are used,but the E-CCE #2 may use a region other than the leftmost region in thePRB pair 2405). For example, one Distributed E-PDCCH may be made up ofthe leftmost (the lowest in the frequency domain) region in a certain DLPRB pair, the second (the second lowest in the frequency) region fromthe left in a certain DL PRB pair, the third (the third lowest in thefrequency) region from the left in a certain DL PRB pair, and the fourth(the fourth lowest in the frequency, the highest in the frequencyregion) region from the left in a certain DL PRB pair.

The present invention can also be applied to a case where one secondPDCCH is made up of one or more DL PRBs. In other words, the presentinvention can also be applied to a case where one second PDCCH region ismade up of a plurality of DL PRBs of only the first slot of a downlinksubframe or a case where one second PDCCH region is made up of aplurality of DL PRBs of only the second slot of a downlink subframe. Ina DL PRB pair configured in a second PDCCH region, all the resourcesexcept the first PDCCH and a downlink reference signal (downlinkresource elements) are not used for a signal of a second PDCCH, and anull configuration may be adopted in which a signal is not mapped insome of the resources (downlink resource elements).

Basically, the first physical resource mapping can be applied in asecond PDCCH region to which precoding processing is applied, and thesecond physical resource mapping can be applied in a second PDCCH regionto which precoding processing is not applied. In the second physicalresource mapping, one E-PDCCH is made up of noncontiguous resources inthe frequency domain, and thus a frequency diversity effect can beobtained.

For the mobile station apparatus 5, one or more second PDCCH regions areconfigured by the base station apparatus 3. For example, for the mobilestation apparatus 5, two second PDCCH regions, including a second PDCCHregion to which the first physical resource mapping is applied andprecoding processing is applied, and a second PDCCH region to which thesecond physical resource mapping is applied and precoding processing isnot applied, are configured. For example, for the mobile stationapparatus 5, only a second PDCCH region to which the second physicalresource mapping is applied and precoding processing is not applied isconfigured. The mobile station apparatus 5 is specified (set,configured) to perform a process of detecting a second PDCCH in thesecond PDCCH region configured by the base station apparatus 3(monitoring). Specification of monitoring of a second PDCCH may beautomatically (implicitly) performed when a second PDCCH region isconfigured for the mobile station apparatus 5, or may be performed bysignaling different from the signaling indicating the configuration of asecond PDCCH region. The same second PDCCH region can be specified for aplurality of mobile station apparatuses 5 by the base station apparatus3.

The information representing the configuration (specification, setting)of a second PDCCH region is transmitted and received between the basestation apparatus 3 and the mobile station apparatus 5 beforecommunication using a second PDCCH is started. For example, theinformation is transmitted and received using RRC (Radio ResourceControl) signaling.

Specifically, the mobile station apparatus 5 receives informationrepresenting the position (assignment) of a DL PRB pair of a secondPDCCH region from the base station apparatus 3. Also, for individualsecond PDCCH regions, information representing the types of physicalresource mapping (first physical resource mapping, second physicalresource mapping) of the second PDCCHs is transmitted from the basestation apparatus 3 to the mobile station apparatus 5. The informationis not necessarily information that explicitly represents the types ofphysical resource mapping of second PDCCHs. Different information may betransmitted from the base station apparatus 3 to the mobile stationapparatus 5, and the types of physical resource mapping of the secondPDCCHs may be implicitly recognized by the mobile station apparatus 5 onthe basis of the information. For example, information representing atransmission method for a second PDCCH in each second PDCCH region istransmitted from the base station apparatus 3 to the mobile stationapparatus 5. In a case where a transmission method to which precodingprocessing is applied is presented, the mobile station apparatus 5determines that the physical resource mapping in the second PDCCH regionis the first physical resource mapping. In a case where a transmissionmethod to which precoding processing is not applied is presented, themobile station apparatus 5 determines that the physical resource mappingin the second PDCCH region is the second physical resource mapping.Alternatively, the physical resource mapping of any of second PDCCHs maybe set as default in the second PDCCH region, and, only in a case wherephysical resource mapping different from the setting is to be used,information representing the situation may be transmitted from the basestation apparatus 3 to the mobile station apparatus 5. The mobilestation apparatus 5 demodulates a signal of a second PDCCH by using aUE-specific RS received in the second PDCCH region configured by thebase station apparatus 3, and performs a process of detecting a secondPDCCH addressed to the mobile station apparatus 5. For example, themobile station apparatus 5 demodulates the signal of the second PDCCH byusing a UE-specific RS in a DL PRB pair to which the resource performingdemodulation belongs.

For the mobile station apparatus 5, candidates (a combination ofcandidates) (candidate set) of an E-CCE aggregation number for LocalizedE-PDCCH may be set (configured) by the base station apparatus 3 for thesecond PDCCH region to which the first physical resource mapping isapplied. For example, for a certain mobile station apparatus 5, E-CCEaggregation 1, E-CCE aggregation 2, and E-CCE aggregation 4 may beconfigured as candidates of an E-CCE aggregation number for theLocalized E-PDCCH for the second PDCCH region to which the firstphysical resource mapping is applied. For example, for a certain mobilestation apparatus 5, E-CCE aggregation 2 and E-CCE aggregation 4 may beconfigured as candidates of an E-CCE aggregation number for theLocalized E-PDCCH for the second PDCCH region to which the firstphysical resource mapping is applied.

Regarding the correspondence between individual E-CCEs in a DL PRB pairand the antenna ports (transmit antennas) corresponding to theindividual E-CCEs, the individual E-CCEs in the DL PRB pair aretransmitted from different antenna ports.

In the second PDCCH region in which a Localized E-PDCCH is mapped, asillustrated in FIG. 20, UE-specific RSs (D1 and D2) for four transmitantennas (antenna port 7, antenna port 8, antenna port 9, and antennaport 10) can be mapped. A plurality of combinations are used as acombination of individual E-CCEs in a DL PRB pair and correspondingantenna ports. In individual combinations, the antenna portscorresponding to individual E-CCEs in a DL PRB pair are different.Signals of individual E-CCEs in a DL PRB pair are transmitted from thecorresponding antenna ports. The antenna ports used for the signals ofE-CCEs are common to the antenna ports used for transmitting UE-specificRSs. For example, four types of combinations (first combination, secondcombination, third combination, and fourth combination) can be used as acombination of individual E-CCEs in a DL PRB pair and the correspondingantenna ports. In the first combination, in FIG. 20, a signal of thesecond PDCCH of E-CCE n is transmitted from the antenna port 7, a signalof the second PDCCH of E-CCE n+1 is transmitted from the antenna port 8,a signal of the second PDCCH of E-CCE n+2 is transmitted from theantenna port 9, and a signal of the second PDCCH of E-CCE n+3 istransmitted from the antenna port 10. In the second combination, in FIG.20, a signal of the second PDCCH of E-CCE n is transmitted from theantenna port 8, a signal of the second PDCCH of E-CCE n+1 is transmittedfrom the antenna port 9, a signal of the second PDCCH of E-CCE n+2 istransmitted from the antenna port 10, and a signal of the second PDCCHof E-CCE n+3 is transmitted from the antenna port 11. In the thirdcombination, in FIG. 20, a signal of the second PDCCH of E-CCE n istransmitted from the antenna port 9, a signal of the second PDCCH ofE-CCE n+1 is transmitted from the antenna port 10, a signal of thesecond PDCCH of E-CCE n+2 is transmitted from the antenna port 7, and asignal of the second PDCCH of E-CCE n+3 is transmitted from the antennaport 8. In the fourth combination, in FIG. 20, a signal of the secondPDCCH of E-CCE n is transmitted from the antenna port 10, a signal ofthe second PDCCH of E-CCE n+1 is transmitted from the antenna port 7, asignal of the second PDCCH of E-CCE n+2 is transmitted from the antennaport 8, and a signal of the second PDCCH of E-CCE n+3 is transmittedfrom the antenna port 9.

Any one of the combinations of individual E-CCEs in a DL PRB pair andcorresponding antenna ports is set for each mobile station apparatus 5by the base station apparatus 3. For example, the setting is performedusing RRC signaling. The base station apparatus 3 transmits signals ofthe individual E-CCEs in the DL PRB pair from the corresponding transmitantennas. That is, the base station apparatus controls the antenna portsused for transmitting the signals of the individual E-CCEs on the basisof the mobile station apparatus 5 to which the signals of individualE-CCEs in the DL PRB pair are to be transmitted. The mobile stationapparatus 5 demodulates the signals of the individual E-CCEs in the DLPRB pair by using UE-specific RSs transmitted from the correspondingtransmit antennas.

For example, in a case where the base station apparatus 3 determinesthat the current state is suitable for MU-MIMO, the base stationapparatus 3 sets, regarding combinations of individual E-CCEs in a DLPRB pair and corresponding antenna ports, different combinations to thesecond PDCCH regions for different mobile station apparatuses 5. Thestate suitable for MU-MIMO is, for example, a state in which the basestation apparatus 3 can apply beamforming (precoding processing) tosignals addressed to different mobile station apparatuses 5 withoutcausing large interference, and there is a request for transmittingsignals of the second PDCCHs to the plurality of mobile stationapparatuses 5 that are geographically separated. For example, it isdifficult to apply beamforming to signals addressed to a plurality ofmobile station apparatuses 5 without causing large interference if theplurality of mobile station apparatuses 5 exist at geographically closepositions. Thus, the base station apparatus 3 does not apply MU-MIMO tosignals of the second PDCCHs addressed to such mobile stationapparatuses 5. The beamforming (precoding) optimal to the performance oftransmit/receive signals is common to the plurality of mobile stationapparatuses 5 existing at geographically close positions. For example,in a case where the base station apparatus 3 determines that the currentstate is unsuitable for MU-MIMO, the base station apparatus 3 sets,regarding combinations of individual E-CCEs in a DL PRB pair andcorresponding antenna ports, the same (common) combination to the secondPDCCH regions for different mobile station apparatuses 5.

A description will be given of processing that is performed in a casewhere the base station apparatus 3 has determined that the current stateis suitable for MU-MIMO. For example, a description will be given of acase where two mobile station apparatuses 5 exist at different positions(for example, area A and area B) in the area covered by the base stationapparatus 3. For convenience of description, the mobile stationapparatus 5 located in area A is referred to as a mobile stationapparatus 5A-1, and the mobile station apparatus 5 located in area B isreferred to as a mobile station apparatus 5B-1. The base stationapparatus 3 sets the first combination for the second PDCCH region ofthe mobile station apparatus 5A-1, regarding combinations of individualE-CCEs in a DL PRB pair and corresponding antenna ports. The basestation apparatus 3 sets the third combination for the second PDCCHregion of the mobile station apparatus 5B-1, regarding combinations ofindividual E-CCEs in a DL PRB pair and corresponding antenna ports.

For example, the base station apparatus 3 transmits a signal of thesecond PDCCH to the mobile station apparatus 5A-1 from the antenna port7 using the resource of the E-CCE n, and transmits a signal of thesecond PDCCH to the mobile station apparatus 5B-1 from the antenna port9 using the resource of the E-CCE n. Here, the base station apparatus 3performs precoding processing suitable for the mobile station apparatus5A-1 on the signal of the second PDCCH to be transmitted from theantenna port 7 and a UE-specific RS, and performs precoding processingsuitable for the mobile station apparatus 5B-1 on the signal of thesecond PDCCH to be transmitted from the antenna port 9 and a UE-specificRS. The mobile station apparatus 5A-1 demodulates the signal of thesecond PDCCH in the resource of the E-CCE n by using the UE-specific RScorresponding to the antenna port 7. The mobile station apparatus 5B-1demodulates the signal of the second PDCCH in the resource of the E-CCEn by using the UE-specific RS corresponding to the antenna port 9. Here,the mobile station apparatus 5A-1 and the mobile station apparatus 5B-1are sufficiently geographically separated from each other, and thus thebase station apparatus 3 can apply beamforming (precoding processing) tothe signals of the second PDCCHs for both the mobile station apparatuses5 without causing large interference. MU-MIMO is realized in theabove-described manner.

For example, the base station apparatus 3 transmits a signal of thesecond PDCCH to the mobile station apparatus 5A-1 from the antenna port7 using the resource of the E-CCE n, transmits a signal of the secondPDCCH to the mobile station apparatus 5A-1 from the antenna port 8 usingthe resource of the E-CCE n+1, transmits a signal of the second PDCCH tothe mobile station apparatus 5B-1 from the antenna port 9 using theresource of the E-CCE n, and transmits a signal of the second PDCCH tothe mobile station apparatus 5B-1 from the antenna port 10 using theresource of the E-CCE n+1. Here, the base station apparatus 3 performsprecoding processing suitable for the mobile station apparatus 5A-1 onthe signals of the second PDCCHs to be transmitted from the antenna port7 and the antenna port 8 and UE-specific RSs, and performs precodingprocessing suitable for the mobile station apparatus 5B-1 on the signalsof the second PDCCHs to be transmitted from the antenna port 9 and theantenna port 10 and UE-specific RSs. The mobile station apparatus 5A-1demodulates the signal of the second PDCCH in the resource of the E-CCEn by using the UE-specific RS corresponding to the antenna port 7, anddemodulates the signal of the second PDCCH in the resource of the E-CCEn+1 by using the UE-specific RS corresponding to the antenna port 8. Themobile station apparatus 5B-1 demodulates the signal of the second PDCCHin the resource of the E-CCE n by using the UE-specific RS correspondingto the antenna port 9, and demodulates the signal of the second PDCCH inthe resource of the E-CCE n+1 by using the UE-specific RS correspondingto the antenna port 10. Here, the mobile station apparatus 5A-1 and themobile station apparatus 5B-1 are sufficiently geographically separatedfrom each other, and thus the base station apparatus 3 can applybeamforming (precoding processing) to the signals of the second PDCCHsfor both the mobile station apparatuses 5 without causing largeinterference. MU-MIMO is realized in the above-described manner.

A description will be given of a case where a mobile station apparatus 5(mobile station apparatus 5A-2) different from the mobile stationapparatus 5A-1 further exists in area A and a mobile station apparatus 5(mobile station apparatus 5B-2) different from the mobile stationapparatus 5B-1 further exists in area B, for example. The base stationapparatus 3 sets the first combination for the second PDCCH region ofthe mobile station apparatus 5A-1, regarding combinations of individualE-CCEs in a DL PRB pair and corresponding antenna ports. The basestation apparatus 3 sets the third combination for the second PDCCHregion of the mobile station apparatus 5A-2, regarding combinations ofindividual E-CCEs in a DL PRB pair and corresponding antenna ports. Thebase station apparatus 3 sets the third combination for the second PDCCHregion of the mobile station apparatus 5B-1, regarding combinations ofindividual E-CCEs in a DL PRB pair and corresponding antenna ports. Thebase station apparatus 3 sets the first combination for the second PDCCHregion of the mobile station apparatus 5B-2, regarding combinations ofindividual E-CCEs in a DL PRB pair and corresponding antenna ports.

For example, the base station apparatus 3 transmits a signal of thesecond PDCCH to the mobile station apparatus 5A-1 from the antenna port7 using the resource of the E-CCE n, and transmits a signal of thesecond PDCCH to the mobile station apparatus 5B-1 from the antenna port9 using the resource of the E-CCE n. The base station apparatus 3transmits a signal of the second PDCCH to the mobile station apparatus5A-2 from the antenna port 8 using the resource of the E-CCE n+3, andtransmits a signal of the second PDCCH to the mobile station apparatus5B-2 from the antenna port 10 using the resource of the E-CCE n+3. Here,the base station apparatus 3 performs precoding processing suitable forthe mobile station apparatus 5A-1 on the signal of the second PDCCH tobe transmitted from the antenna port 7 and a UE-specific RS, performsprecoding processing suitable for the mobile station apparatus 5A-2 onthe signal of the second PDCCH to be transmitted from the antenna port 8and a UE-specific RS, performs precoding processing suitable for themobile station apparatus 5B-1 on the signal of the second PDCCH to betransmitted from the antenna port 9 and a UE-specific RS, and performsprecoding processing suitable for the mobile station apparatus 5B-2 onthe signal of the second PDCCH to be transmitted from the antenna port10 and a UE-specific RS. The mobile station apparatus 5A-1 demodulatesthe signal of the second PDCCH in the resource of the E-CCE n by usingthe UE-specific RS corresponding to the antenna port 7. The mobilestation apparatus 5A-2 demodulates the signal of the second PDCCH in theresource of the E-CCE n+3 by using the UE-specific RS corresponding tothe antenna port 8. The mobile station apparatus 5B-1 demodulates thesignal of the second PDCCH in the resource of the E-CCE n by using theUE-specific RS corresponding to the antenna port 9. The mobile stationapparatus 5B-2 demodulates the signal of the second PDCCH in theresource of the E-CCE n+3 by using the UE-specific RS corresponding toantenna port 10. Here, the mobile station apparatus 5A-1 and the mobilestation apparatus 5B-1 are sufficiently geographically separated fromeach other, and thus the base station apparatus 3 can apply beamforming(precoding processing) to the signals of the second PDCCHs for both themobile station apparatuses 5 without causing large interference. Also,the mobile station apparatus 5A-2 and the mobile station apparatus 5B-2are sufficiently geographically separated from each other, and thus thebase station apparatus 3 can apply beamforming (precoding processing) tothe signals of the second PDCCHs for both the mobile station apparatuses5 without causing large interference. MU-MIMO is realized in theabove-described manner.

For example, the base station apparatus 3 transmits a signal of thesecond PDCCH to the mobile station apparatus 5A-1 from the antenna port7 using the resource of the E-CCE n, transmits a signal of the secondPDCCH to the mobile station apparatus 5A-1 from the antenna port 8 usingthe resource of the E-CCE n+1, transmits a signal of the second PDCCH tothe mobile station apparatus 5A-2 from the antenna port 7 using theresource of the E-CCE n+2, transmits a signal of the second PDCCH to themobile station apparatus 5A-2 from the antenna port 8 using the resourceof the E-CCE n+3, transmits a signal of the second PDCCH to the mobilestation apparatus 5B-1 from the antenna port 9 using the resource of theE-CCE n, transmits a signal of the second PDCCH to the mobile stationapparatus 5B-1 from the antenna port 10 using the resource of the E-CCEn+1, transmits a signal of the second PDCCH to the mobile stationapparatus 5B-2 from the antenna port 9 using the resource of the E-CCEn+2, and transmits a signal of the second PDCCH to the mobile stationapparatus 5B-2 from the antenna port 10 using the resource of the E-CCEn+3. Here, the base station apparatus 3 performs precoding processingsuitable for the mobile station apparatus 5A-1 and the mobile stationapparatus 5A-2 on the signals of the second PDCCHs to be transmittedfrom the antenna port 7 and the antenna port 8 and UE-specific RSs, andperforms precoding processing suitable for the mobile station apparatus5B-1 and the mobile station apparatus 5B-2 on the signals of the secondPDCCHs to be transmitted from the antenna port 9 and the antenna port 10and UE-specific RSs. The mobile station apparatus 5A-1 demodulates thesignal of the second PDCCH in the resource of the E-CCE n by using theUE-specific RS corresponding to the antenna port 7, and demodulates thesignal of the second PDCCH in the resource of the E-CCE n+1 by using theUE-specific RS corresponding to the antenna port 8. The mobile stationapparatus 5A-2 demodulates the signal of the second PDCCH in theresource of the E-CCE n+2 by using the UE-specific RS corresponding tothe antenna port 7, and demodulates the signal of the second PDCCH inthe resource of the E-CCE n+3 by using the UE-specific RS correspondingto the antenna port 8. The mobile station apparatus 5B-1 demodulates thesignal of the second PDCCH in the resource of the E-CCE n by using theUE-specific RS corresponding to the antenna port 9, and demodulates thesignal of the second PDCCH in the resource of the E-CCE n+1 by using theUE-specific RS corresponding to the antenna port 10. The mobile stationapparatus 5B-2 demodulates the signal of the second PDCCH in theresource of the E-CCE n+2 by using the UE-specific RS corresponding tothe antenna port 9, and demodulates the signal of the second PDCCH inthe resource of the E-CCE n+3 by using the UE-specific RS correspondingto the antenna port 10. Here, the mobile station apparatus 5A-1 and themobile station apparatus 5A-2 are sufficiently geographically separatedfrom the mobile station apparatus 5B-1 and the mobile station apparatus5B-2, and thus the base station apparatus 3 can apply beamforming(precoding processing) to the signals of the second PDCCHs for themobile station apparatuses 5 located in the different areas withoutcausing large interference. Further, the mobile station apparatus 5A-1and the mobile station apparatus 5A-2 are sufficiently geographicallyclose to each other (in area A), and thus suitable beamforming(precoding processing) is common thereto. Thus, the base stationapparatus 3 can efficiently transmit the signals of the second PDCCHs toboth the mobile station apparatus 5A-1 and the mobile station apparatus5A-2 using the same antenna ports (antenna port 7 and antenna port 8).Also, the mobile station apparatus 5B-1 and the mobile station apparatus5B-2 are sufficiently geographically close to each other (in area B),and thus suitable beamforming (precoding processing) is common thereto.Thus, the base station apparatus 3 can efficiently transmit the signalsof the second PDCCHs to both the mobile station apparatus 5B-1 and themobile station apparatus 5B-2 using the same antenna ports (antenna port9 and antenna port 10). MU-MIMO is realized in the above-describedmanner.

A description will be given of processing that is performed in a casewhere the base station apparatus 3 has determined that the current stateis not suitable for MU-MIMO. For example, a description will be given ofa case where four mobile station apparatuses 5 exist at differentpositions (for example, area C, area D, area E, and area F) within thearea covered by the base station apparatus 3. For convenience ofdescription, the mobile station apparatus 5 located in area C isreferred to as a mobile station apparatus 5C-1, the mobile stationapparatus 5 located in area D is referred to as a mobile stationapparatus 5D-1, the mobile station apparatus 5 located in area E isreferred to as a mobile station apparatus 5E-1, and the mobile stationapparatus 5 located in area F is referred to as a mobile stationapparatus 5F-1. Here, a description will be given of a case where areaC, area D, area E, and area F are not sufficiently separated from oneanother, it is difficult to apply beamforming (precoding processing) tosignals of the second PDCCHs for the mobile station apparatuses 5located in the individual areas without causing large interference, andit is difficult to apply MU-MIMO. Also, a description will be given of acase where area C, area D, area E, and area F are not very close to oneanother, and beamforming (precoding processing) suitable for the signalsof the second PDCCHs for the mobile station apparatuses 5 located in theindividual areas varies. The base station apparatus 3 sets the firstcombination to the second PDCCH region for the mobile station apparatus5C-1, the second PDCCH region for the mobile station apparatus 5D-1, thesecond PDCCH region for the mobile station apparatus 5E-1, and thesecond PDCCH region for the mobile station apparatus 5F-1, regardingcombinations of individual E-CCEs in a DL PRB pair and correspondingantenna ports.

For example, the base station apparatus 3 transmits a signal of thesecond PDCCH to the mobile station apparatus 5C-1 from the antenna port7 using the resource of the E-CCE n, transmits a signal of the secondPDCCH to the mobile station apparatus 5D-1 from the antenna port 8 usingthe resource of the E-CCE n+1, transmits a signal of the second PDCCH tothe mobile station apparatus 5E-1 from the antenna port 9 using theresource of the E-CCE n+2, and transmits a signal of the second PDCCH tothe mobile station apparatus 5F-1 from the antenna port 10 using theresource of the E-CCE n. Here, the base station apparatus 3 performsprecoding processing suitable for the mobile station apparatus 5C-1 onthe signal of the second PDCCH to be transmitted from the antenna port 7and a UE-specific RS, performs precoding processing suitable for themobile station apparatus 5D-1 on the signal of the second PDCCH to betransmitted from the antenna port 8 and a UE-specific RS, performsprecoding processing suitable for the mobile station apparatus 5E-1 onthe signal of the second PDCCH to be transmitted from the antenna port 9and a UE-specific RS, and performs precoding processing suitable for themobile station apparatus 5F-1 on the signal of the second PDCCH to betransmitted from the antenna port 10 and a UE-specific RS. The mobilestation apparatus 5C-1 demodulates the signal of the second PDCCH in theresource of the E-CCE n by using the UE-specific RS corresponding to theantenna port 7. The mobile station apparatus 5D-1 demodulates the signalof the second PDCCH in the resource of the E-CCE n+1 by using theUE-specific RS corresponding to the antenna port 8. The mobile stationapparatus 5E-1 demodulates the signal of the second PDCCH in theresource of the E-CCE n+2 by using the UE-specific RS corresponding tothe antenna port 9. The mobile station apparatus 5F-1 demodulates thesignal of the second PDCCH in the resource of the E-CCE n+3 by using theUE-specific RS corresponding to the antenna port 10. As described above,the base station apparatus 3 can independently perform suitablebeamforming (precoding processing) on the individual signals of thesecond PDCCHs for the mobile station apparatuses 5 located in theindividual areas. Accordingly, requirements can be fulfilled regardingthe performance of the signals of the second PDCCHs for the mobilestation apparatuses 5 located in the individual areas.

In a case where area C, area D, area E, and area F are separated fromone another, beamforming (precoding processing) can be applied to thesignals of the second PDCCHs for the mobile station apparatuses 5located in the individual areas without causing large interference, andMU-MIMO can be applied, the base station apparatus 3 may set the firstcombination for the second PDCCH region of the mobile station apparatus5C-1, the second combination for second PDCCH region of the mobilestation apparatus 5D-1, the third combination for the second PDCCHregion of the mobile station apparatus 5E-1, and the fourth combinationfor the second PDCCH region of the mobile station apparatus 5F-1,regarding combinations of individual E-CCEs in a DL PRB pair andcorresponding antenna ports.

Hereinafter, a control signal mapped to a second PDCCH will bedescribed. A control signal mapped to a second PDCCH is processed foreach piece of control information regarding one mobile station apparatus5, and can be subjected to scramble processing, modulation processing,layer mapping processing, precoding processing, and so forth, like adata signal. Here, layer mapping processing means part of MIMO signalprocessing, which is performed in a case where multi-antennatransmission is applied to a second PDCCH. For example, layer mappingprocessing is performed on the second PDCCH to which precodingprocessing is applied, and the second PDCCH to which precodingprocessing is not applied but transmission diversity is applied.Further, a control signal mapped to a second PDCCH can be subjected tocommon precoding processing together with a UE-specific RS. At thistime, it is preferable that precoding processing be performed withfavorable precoding weights in units of mobile station apparatuses 5.

A UE-specific RS is multiplexed, by the base station apparatus 3, with aDL PRB pair to which a second PDCCH is mapped. The mobile stationapparatus 5 demodulates the signal of the second PDCCH by using theUE-specific RS. For the UE-specific RS used to demodulate the secondPDCCH, different combinations can be set in individual second PDCCHregions regarding combinations of individual E-CCEs in a DL PRB pair andcorresponding antenna ports. That is, different combinations can be setfor individual mobile station apparatuses 5 regarding combinations ofindividual E-CCEs in the DL PRB pair in the second PDCCH region andcorresponding antenna ports. In the second PDCCH region to which thefirst physical resource mapping is applied, UE-specific RSs for aplurality of transmit antennas (antenna port 7, antenna port 8, antennaport 9, and antenna port 10) are mapped. In the second PDCCH region towhich the second physical resource mapping is applied, a UE-specific RSfor one transmit antenna (antenna port 7) is mapped. In the second PDCCHregion to which the second physical resource mapping is applied, in acase where transmission diversity such as SFBC (Space Frequency BlockCoding) is applied to Distributed E-PDCCH, UE-specific RSs for twotransmit antennas (antenna port 7 and antenna port 8) may be mapped.

In the second PDCCH region to which the first physical resource mappingis applied, individual E-CCEs in a DL PRB pair correspond to differenttransmit antennas, and signals are transmitted from the correspondingtransmit antennas. In the second PDCCH region to which the secondphysical resource mapping is applied, individual E-CCEs in a DL PRB paircorrespond to the same (common) transmit antennas, and signals aretransmitted from the corresponding transmit antennas.

For example, in the second PDCCH region to which the first physicalresource mapping is applied, the first combination, the secondcombination, the third combination, or the fourth combination can beused regarding combinations of individual E-CCEs in a DL PRB pair andcorresponding antenna ports. That is, any one of the plurality ofcombinations is set (configured) for each mobile station apparatus 5. Inthe first combination, in FIG. 20, a signal of the second PDCCH of theE-CCE n is transmitted from the antenna port 7, a signal of the secondPDCCH of the E-CCE n+1 is transmitted from the antenna port 8, a signalof the second PDCCH of the E-CCE n+2 is transmitted from the antennaport 9, and a signal of the second PDCCH of the E-CCE n+3 is transmittedfrom the antenna port 10. In the second combination, in FIG. 20, asignal of the second PDCCH of the E-CCE n is transmitted from theantenna port 8, a signal of the second PDCCH of the E-CCE n+1 istransmitted from the antenna port 9, a signal of the second PDCCH of theE-CCE n+2 is transmitted from the antenna port 10, and a signal of thesecond PDCCH of the E-CCE n+3 is transmitted from the antenna port 11.In the third combination, in FIG. 20, a signal of the second PDCCH ofthe E-CCE n is transmitted from the antenna port 9, a signal of thesecond PDCCH of the E-CCE n+1 is transmitted from the antenna port 10, asignal of the second PDCCH of the E-CCE n+2 is transmitted from theantenna port 7, and a signal of the second PDCCH of the E-CCE n+3 istransmitted from the antenna port 8. In the fourth combination, in FIG.20, a signal of the second PDCCH of E-CCE n is transmitted from theantenna port 10, a signal of the second PDCCH of the E-CCE n+1 istransmitted from the antenna port 7, a signal of the second PDCCH of theE-CCE n+2 is transmitted from the antenna port 8, and a signal of thesecond PDCCH of the E-CCE n+3 is transmitted from the antenna port 9.

Here, the relationship among the first combination, the secondcombination, the third combination, and the fourth combination may bereferred to as a relationship in which the antenna ports correspondingto individual E-CCEs in a DL PRB pair are shifted. A description will begiven of the relationship between the first combination and the thirdcombination. A plurality of E-CCEs in a DL PRB pair can be grouped intoa plurality of groups (sets), for example, two groups (group A and groupB). The relationship between the first combination and the thirdcombination may be referred to as a relationship in which a set ofantenna ports corresponding to individual E-CCEs in a group is switchedbetween groups. More specifically, the antenna port set (antenna port 7and antenna port 8) corresponding to group A of the first combination(E-CCE n and E-CCE n+1 in FIG. 20) is the same as the antenna port set(antenna port 7 and antenna port 8) corresponding to group B of thethird combination (E-CCE n+2 and E-CCE n+3 in FIG. 20), and the antennaport set (antenna port 9 and antenna port 10) corresponding to group Bof the first combination (E-CCE n+2 and E-CCE n+3 in FIG. 20) is thesame as the antenna port set (antenna port 9 and antenna port 10)corresponding to group A of the third combination (E-CCE n and E-CCE n+1in FIG. 20). The relationship between the second combination and thefourth combination is the same as the relationship between the firstcombination and the third combination.

A predetermined scramble ID may be used to generate a UE-specific RS tobe mapped in a second PDCCH region. For example, as a scramble ID usedfor a UE-specific RS, a value of any one of 0 to 3 may be specified.

FIG. 29 is a diagram illustrating monitoring of second PDCCHs of themobile station apparatus 5 according to the embodiment of the presentinvention. A plurality of second PDCCH regions (second PDCCH region 1and second PDCCH region 2) are configured for the mobile stationapparatus 5. For the mobile station apparatus 5, a search space isconfigured in each of the second PDCCH regions. The search space means alogical region in which the mobile station apparatus 5 performs decodingand detection of a second PDCCH in a second PDCCH region. The searchspace is made up of a plurality of second PDCCH candidates. The secondPDCCH candidates are targets on which the mobile station apparatus 5performs decoding and detection of a second PDCCH. For each E-CCEaggregation number, different second PDCCH candidates are made up ofdifferent E-CCEs (including one E-CCE and a plurality of E-CCEs). TheE-CCEs constituting a plurality of second PDCCH candidates of a searchspace that is configured in the second PDCCH region to which the firstphysical resource mapping is applied are a plurality of E-CCEs made upof contiguous regions. The E-CCEs constituting a plurality of secondPDCCH candidates of a search space that is configured in the secondPDCCH region to which the second physical resource mapping is appliedare a plurality of E-CCEs made up of noncontiguous regions. The firstE-CCE number used for a search space in the second PDCCH region is setfor each mobile station apparatus 5. For example, with a random functionusing an identifier assigned to the mobile station apparatus 5 (mobilestation identifier), the first E-CCE number used for a search space isset. For example, the base station apparatus 3 notifies the mobilestation apparatus 5 of the first E-CCE number used for a search space byusing RRC signaling.

A plurality of search spaces (first search space and second searchspace) are configured for the mobile station apparatus 5 for which aplurality of second PDCCH regions are configured. The first physicalresource mapping is applied to part of a plurality of second PDCCHregions (second PDCCH region 1) configured for the mobile stationapparatus 5, and the second physical resource mapping is applied toanother part of the plurality of second PDCCH regions (second PDCCHregion 2).

The number of second PDCCH candidates in the first search space can bedifferent from the number of second PDCCH candidates in the secondsearch space. For example, in order to perform control so that a secondPDCCH to which precoding processing is applied is basically used, and asecond PDCCH to which precoding processing is not applied and which hasa frequency diversity effect is used in a case where it is difficult inthe base station apparatus 3 to realize appropriate precoding processingdue to a certain situation, the number of second PDCCH candidates in thefirst search space may be set to be larger than the number of secondPDCCH candidates in the second search space.

In a certain E-CCE aggregation number, the number of second PDCCHcandidates in the first search space can be the same as the number ofsecond PDCCH candidates in the second search space. In another E-CCEaggregation number, the number of second PDCCH candidates in the firstsearch space can be different from the number of second PDCCH candidatesin the second search space. In a certain E-CCE aggregation number, thenumber of second PDCCH candidates in the first search space can belarger than the number of second PDCCH candidates in the second searchspace. In another E-CCE aggregation number, the number of second PDCCHcandidates in the first search space can be smaller than the number ofsecond PDCCH candidates in the second search space.

Further, second PDCCH candidates of a certain E-CCE aggregation numbermay be set to the search space of one of the second PDCCH regions, andmay not be set to the search space of another one of the second PDCCHregions.

The number of second PDCCH candidates in the search space in one secondPDCCH region can be changed on the basis of the number of second PDCCHregions configured for the mobile station apparatus 5. For example, asthe number of second PDCCH regions configured for the mobile stationapparatus 5 increases, the number of second PDCCH candidates in thesearch space in one second PDCCH region is decreased.

<Overall Configuration of Base Station Apparatus 3>

The configuration of the base station apparatus 3 according to theembodiment will be described with reference to FIGS. 1, 2, and 3. FIG. 1is a schematic block diagram illustrating the configuration of the basestation apparatus 3 according to the embodiment of the presentinvention. As illustrated in FIG. 1, the base station apparatus 3includes a reception processor (second reception processor) 101, a radioresource controller (second radio resource controller) 103, a controller(second controller) 105, and a transmission processor (secondtransmission processor) 107.

The reception processor 101 demodulates, using a UL RS, receive signalson the PUCCH and PUSCH received by a receive antenna 109 from the mobilestation apparatus 5, decodes the signal, and extracts controlinformation and information data, in response to an instruction from thecontroller 105. The reception processor 101 performs a process ofextracting UCI on the uplink subframe and UL PRB in which the basestation apparatus 3 assigns the resource of the PUCCH to the mobilestation apparatus 5. The reception processor 101 receives, from thecontroller 105, an instruction indicating which process is to beperformed on which uplink subframe and which UL PRB. For example, thereception processor 101 receives, from the controller 105, aninstruction to perform a detection process in which multiplication andcombining of code sequences in the time domain and multiplication andcombining of code sequences in the frequency domain are performed on asignal on the PUCCH for an ACK/NACK (PUCCH format 1a, PUCCH format 1b).Also, the reception processor 101 receives, from the controller 105, acode sequence in the frequency domain and/or a code sequence in the timedomain to be used for a process of detecting UCI from the PUCCH. Thereception processor 101 outputs the extracted UCI to the controller 105,and outputs information data to a higher layer. The details of thereception processor 101 will be described below.

Also, the reception processor 101 detects (receives) a preamble sequencefrom a receive signal on the PRACH received by the receive antenna 109from the mobile station apparatus 5, in response to an instruction fromthe controller 105. Further, the reception processor 101 performsestimation of arrival timing (reception timing) together with detectionof the preamble sequence. The reception processor 101 performs a processof detecting a preamble sequence on the uplink subframe and UL PRB pairto which the base station apparatus 3 has allocated the resource of thePRACH. The reception processor 101 outputs information regarding theestimated arrival timing to the controller 105.

Further, the reception processor 101 measures the channel quality of oneor more UL PRBs (UL PRB pairs) by using the SRS received from the mobilestation apparatus 5. Also, the reception processor 101 detects(calculates, measures) an out-of-synchronization state in the uplink byusing the SRS received from the mobile station apparatus 5. Thereception processor 101 receives, from the controller 105, aninstruction indicating which process is to be performed on which uplinksubframe and which UL PRB (UL PRB pair). The reception processor 101outputs information regarding the measured channel quality and thedetected out-of-synchronization state of the uplink to the controller105. The details of the reception processor 101 will be described below.

The radio resource controller 103 sets assignment of resources to thePDCCHs (first PDCCH, second PDCCH), assignment of resources to thePUCCH, assignment of a DL PRB pair to the PDSCH, assignment of a UL PRBpair to the PUSCH, assignment of resources to the PRACH, assignment ofresources to the SRS, various channel modulation schemes/codingrates/transmit power control values/phase rotation amounts (weightingvalues) to be used in precoding processing, phase rotation amounts(weighting values) to be used in precoding processing of a UE-specificRS, and so forth. The radio resource controller 103 also sets a codesequence in the frequency domain and a code sequence in the time domainfor the PUCCH and so forth. Also, the radio resource controller 103 setsa plurality of second PDCCH regions, and sets DL PRB pairs to be usedfor the individual second PDCCH regions. Also, the radio resourcecontroller 103 sets the physical resource mapping of the individualsecond PDCCH regions. Also, the radio resource controller 103 sets, forthe second PDCCH region, a combination of individual E-CCEs in a DL PRBpair and corresponding antenna ports. Specifically, the radio resourcecontroller 103 sets the transmit antennas for transmitting signals onthe individual E-CCEs in the DL PRB pair. Part of the information set bythe radio resource controller 103 is reported to the mobile stationapparatus 5 via the transmission processor 107, for example, informationrepresenting a DL PRB pair in a second PDCCH region, informationrepresenting the physical resource mapping in the second PDCCH region(information representing first physical resource mapping or secondphysical resource mapping), information representing a combination ofindividual E-CCEs in the DL PRB pair and corresponding antenna ports(first combination, second combination, third combination, or fourthcombination), and information representing a resource block pair that ispossibly used for the second PDCCH (for example, a bit map), arereported to the mobile station apparatus 5.

Further, the radio resource controller 103 sets assignment of radioresources of the PDSCH on the basis of the UCI that has been obtained bythe reception processor 101 using the PUCCH and that has been input viathe controller 105. For example, in a case where an ACK/NACK obtainedusing the PUCCH is input, the radio resource controller 103 performs,for the mobile station apparatus 5, assignment of resources of the PDSCHin which a NACK is indicated by the ACK/NACK.

The radio resource controller 103 outputs various control signals to thecontroller 105. Examples of the control signals include a control signalrepresenting the physical resource mapping of a second PDCCH region, acontrol signal representing transmit antennas for transmitting signalson individual E-CCEs in the DL PRB pair in the second PDCCH region, acontrol signal representing assignment of resources of the second PDCCH,and a control signal representing a phase rotation amount to be used forprecoding processing.

The controller 105 performs, for the transmission processor 107, controlfor assignment of a DL PRB pair to a PDSCH, assignment of resources to aPDCCH, setting of a modulation scheme for the PDSCH, setting of codingrates for the PDSCH and PDCCH (E-CCE aggregation number of the secondPDCCH), setting of a UE-specific RS in a second PDCCH region, setting ofa transmit antenna for transmitting a signal on an E-CCE, setting ofprecoding processing to the PDSCH, PDCCH, and a UE-specific RS, and soforth on the basis of a control signal received from the radio resourcecontroller 103. Also, the controller 105 generates DCI to be transmittedusing the PDCCH and outputs it to the transmission processor 107, on thebasis of a control signal received from the radio resource controller103. The DCI transmitted using the PDCCH may be a downlink assignment oran uplink grant. Also, the controller 105 performs control so as totransmit, to the mobile station apparatus 5 via the transmissionprocessor 107 using the PDSCH, information representing a second PDCCHregion, information representing physical resource mapping of the secondPDCCH region, information representing a combination of individualE-CCEs in the DL PRB pair and corresponding antenna ports (firstcombination, second combination, third combination, or fourthcombination), a bit map indicating resource block pairs that arepossibly used for the second control channel, and so forth.

The controller 105 performs, for the reception processor 101, controlfor assignment of a UL PRB pair to a PUSCH, assignment of resources to aPUCCH, setting of modulation schemes of the PUSCH and PUCCH, setting ofthe coding rate of the PUSCH, a detection process for the PUCCH, settingof a code sequence for the PUCCH, assignment of resources to the PRACH,assignment of resources to the SRS, and so forth, on the basis of acontrol signal received from the radio resource controller 103. Also,the controller 105 receives, from the reception processor 101, UCItransmitted from the mobile station apparatus 5 using the PUCCH, andoutputs the received UCI to the radio resource controller 103.

Also, the controller 105 receives, from the reception processor 101,information representing the arrival timing of a detected preamblesequence and information representing an out-of-synchronization state ofthe uplink detected from the received SRS, and calculates an adjustmentvalue of transmission timing in the uplink (TA: Timing Advance, TimingAdjustment, Timing Alignment) (TA value). Information representing thecalculated adjustment value of the transmission timing in the uplink (TAcommand) is reported to the mobile station apparatus 5 via thetransmission processor 107.

The transmission processor 107 generates signals to be transmitted usingthe PDCCH and PDSCH on the basis of a control signal received from thecontroller 105, and transmits the signals via the transmit antenna 111.The transmission processor 107 transmits, to the mobile stationapparatus 5, information representing a second PDCCH region, informationrepresenting the physical resource mapping of the second PDCCH region,information representing a combination of individual E-CCEs in a DL PRBpair and corresponding antenna ports (first combination, secondcombination, third combination, or fourth combination), information datareceived from a higher layer, and so forth received from the radioresource controller 103, by using the PDSCH. Also, the transmissionprocessor 107 transmits the DCI received from the controller 105 to themobile station apparatus 5 by using the PDCCH (first PDCCH, secondPDCCH). Also, the transmission processor 107 transmits a CRS, aUE-specific RS, and a CSI-RS. To simplify the description, hereinafterit is assumed that information data includes information regardingseveral types of control. The details of the transmission processor 107will be described below.

<Configuration of Transmission Processor 107 of Base Station Apparatus3>

Hereinafter, the details of the transmission processor 107 of the basestation apparatus 3 will be described. FIG. 2 is a schematic blockdiagram illustrating the configuration of the transmission processor 107of the base station apparatus 3 according to the embodiment of thepresent invention. As illustrated in FIG. 2, the transmission processor107 includes a plurality of physical downlink shared channel processors201-1 to 201-M (hereinafter the physical downlink shared channelprocessors 201-1 to 201-M are collectively referred to as physicaldownlink shared channel processors 201), a plurality of physicaldownlink control channel processors 203-1 to 203-M (hereinafter thephysical downlink control channel processors 203-1 to 203-M arecollectively referred to as physical downlink control channel processors203), a downlink pilot channel processor 205, a precoding processor 231,a multiplexer 207, an IFFT (Inverse Fast Fourier Transform) unit 209, aGI (Guard Interval) insertion unit 211, a D/A (Digital/Analog converter)unit 213, a transmission RF (Radio Frequency) unit 215, and the transmitantenna 111. The individual physical downlink shared channel processors201 and the individual physical downlink control channel processors 203have the same configuration and function, and thus one of them will bedescribed. To simplify the description, it is assumed that the transmitantenna 111 includes a plurality of antenna ports (antenna ports 0 to22).

As illustrated in FIG. 2, each of the physical downlink shared channelprocessors 201 includes a turbo encoder 219, a data modulator 221, and aprecoding processor 229. Also, as illustrated in FIG. 2, each of thephysical downlink control channel processors 203 includes aconvolutional encoder 223, a QPSK modulator 225, and a precodingprocessor 227. The physical downlink shared channel processor 201performs baseband signal processing to transmit information data to themobile station apparatus 5 using the OFDM scheme. The turbo encoder 219performs, on the information data input thereto, turbo coding toincrease the error resilience of the data at the coding rate receivedfrom the controller 105, and outputs the information data to the datamodulator 221. The data modulator 221 modulates the data coded by theturbo encoder 219 by using the modulation scheme received from thecontroller 105, for example, QPSK (Quadrature Phase Shift Keying), 16QAM(16 Quadrature Amplitude Modulation), and 64QAM (64 Quadrature AmplitudeModulation), and generates a signal sequence of modulation symbols. Thedata modulator 221 outputs the generated signal sequence to theprecoding processor 229. The precoding processor 229 performs precodingprocessing (beamforming processing) on the signal received from the datamodulator 221, and outputs the signal to the multiplexer 207. Here, inthe precoding processing, it is preferable that phase rotation or thelike be performed on a signal to be generated so that the mobile stationapparatus 5 can efficiently receive the signal (for example, so that thereceive power is maximized and interference is minimized). In the caseof not performing precoding processing on a signal received from thedata modulator 221, the precoding processor 229 outputs the signalreceived from the data modulator 221 to the multiplexer 207 withoutperforming any processing.

The physical downlink control channel processor 203 performs basebandsignal processing so as to transmit DCI received from the controller 105using the OFDM scheme. The convolutional encoder 223 performsconvolutional coding to increase the error resilience of the DCI on thebasis of the coding rate received from the controller 105. Here, the DCIis controlled in units of bits. The coding rate of the DCI transmittedon the second PDCCH relates to an E-CCE aggregation number that is set.Also, the convolutional encoder 223 performs, on the basis of the codingrate received from the controller 105, rate matching to adjust thenumber of output bits with respect to the bits on which processing ofconvolutional coding has been performed. The convolutional encoder 223outputs the encoded DCI to the QPSK modulator 225. The QPSK modulator225 modulates the DCI encoded by the convolutional encoder 223 by usingthe QPSK modulation scheme, and outputs a signal sequence of themodulated modulation symbols to the precoding processor 227. Theprecoding processor 227 performs precoding processing on the signalreceived from the QPSK modulator 225 and outputs the signal to themultiplexer 207. The precoding processor 227 may output the signalreceived from the QPSK modulator 225 to the multiplexer 207 withoutperforming precoding processing thereon.

The downlink pilot channel processor 205 generates downlink referencesignals (CRS, UE-specific RS, CSI-RS) which are signals known in themobile station apparatus 5, and outputs them to the precoding processor231. The precoding processor 231 does not perform precoding processingon the CRS, CSI-RS, and part of UE-specific RS received from thedownlink pilot channel processor 205, and outputs them to themultiplexer 207. For example, a UE-specific RS on which precodingprocessing is not performed by the precoding processor 231 is aUE-specific RS in a DL PRB pair used for a second PDCCH in the secondPDCCH region of the second physical resource mapping. The precodingprocessor 231 performs precoding processing on the part of theUE-specific RS received from the downlink pilot channel processor 205,and outputs it to the multiplexer 207. For example, a UE-specific RS onwhich precoding processing is performed by the precoding processor 231is a UE-specific RS in a DL PRB pair used for a second PDCCH in thesecond PDCCH region of the first physical resource mapping. Theprecoding processor 231 performs, on part of the UE-specific RS, aprocess similar to the process performed on the PDSCH in the precodingprocessor 229 and/or the processing performed on the second PDCCH in theprecoding processor 227. More specifically, the precoding processor 231performs precoding processing on a signal on a certain E-CCE, and alsoperforms similar precoding processing on the UE-specific RS whoseantenna port corresponds to the E-CCE. Thus, in the case of demodulatinga signal of the second PDCCH to which precoding processing is applied inthe mobile station apparatus 5, the UE-specific RS can be used toestimate an equalization channel in which channel variations in thedownlink is combined with phase rotation by the precoding processor 227.That is, the base station apparatus 3 need not notify the mobile stationapparatus 5 of information about the precoding processing (the amount ofphase rotation) by the precoding processor 227, and the mobile stationapparatus 5 is capable of demodulating the signal subjected to theprecoding processing.

In a case where precoding processing is not used for the PDSCH andsecond PDCCH on which demodulation processing such as channelcompensation is performed using a UE-specific RS, the precodingprocessor 231 outputs the UE-specific RS to the multiplexer 207 withoutperforming precoding processing on the UE-specific RS.

The multiplexer 207 multiplexes a signal received from the downlinkpilot channel processor 205, signals received from the individualphysical downlink shared channel processors 201, and signals receivedfrom the individual physical downlink control channel processors 203 ona downlink subframe in response to an instruction from the controller105. Control signals regarding assignment of a DL PRB pair to the PDSCHset by the radio resource controller 103, assignment of resources toPDCCHs (first PDCCH, second PDCCH), and physical resource mapping in thesecond PDCCH region are input to the controller 105, and the controller105 controls the processing in the multiplexer 207 on the basis of thecontrol signals. For example, the multiplexer 207 multiplexes a signalof the second PDCCH on a downlink resource using the E-CCE aggregationnumber set by the radio resource controller 103. The multiplexer 207outputs the multiplexed signal to the IFFT unit 209.

The IFFT unit 209 performs inverse fast Fourier transform on themultiplexed signal generated by the multiplexer 207, performs modulationthereon using the OFDM scheme, and outputs it to the GI insertion unit211. The GI insertion unit 211 adds guard interval to the signalmodulated in the OFDM scheme by the IFFT unit 209, thereby generating abaseband digital signal made up of symbols in the OFDM scheme. As isknown, guard interval is generated by duplicating part of the head orend of the OFDM symbols to be transmitted. The GI insertion unit 211outputs the generated baseband digital signal to the D/A unit 213. TheD/A unit 213 converts the baseband digital signal received from the GIinsertion unit 211 into an analog signal, and outputs the analog signalto the transmission RF unit 215. The transmission RF unit 215 generatesin-phase components and orthogonal components of an intermediatefrequency from the analog signal received from the D/A unit 213, andremoves extra frequency components for the intermediate frequency band.Subsequently, the transmission RF unit 215 converts (up-converts) theintermediate-frequency signal into a high-frequency signal, removesextra frequency components, amplifies the power, and transmits thesignal to the mobile station apparatus 5 via the transmit antenna 111.

<Configuration of Reception Processor 101 of Base Station Apparatus 3>

Hereinafter, the reception processor 101 of the base station apparatus 3will be described in detail. FIG. 3 is a schematic block diagramillustrating the configuration of the reception processor 101 of thebase station apparatus 3 according to the embodiment of the presentinvention. As illustrated in FIG. 3, the reception processor 101includes a reception RF unit 301, an A/D (Analog/Digital converter) unit303, a symbol timing detector 309, a GI remover 311, an FFT unit 313, asubcarrier demapping unit 315, a channel estimator 317, a PUSCH channelequalizer 319, a PUCCH channel equalizer 321, an IDFT unit 323, a datademodulator 325, a turbo decoder 327, a physical uplink control channeldetector 329, a preamble detector 331, and an SRS processor 333.

The reception RF unit 301 appropriately amplifies a signal received bythe receive antenna 109, converts (down-converts) the signal into anintermediate frequency, removes unnecessary frequency components,controls the amplification level so that the signal level isappropriately kept, and performs orthogonal demodulation on the basis ofthe in-phase components and orthogonal components of the receivedsignal. The reception RF unit 301 outputs the analog signal subjected toorthogonal demodulation to the A/D unit 303. The A/D unit 303 convertsthe analog signal subjected to the orthogonal demodulation in thereception RF unit 301 into a digital signal, and outputs the digitalsignal resulting from the conversion to the symbol timing detector 309and the GI remover 311.

The symbol timing detector 309 detects the timing of a symbol on thebasis of a signal received from the A/D unit 303, and outputs a controlsignal representing the detected timing of a symbol boundary to the GIremover 311. The GI remover 311 removes a part corresponding to guardinterval from the signal received from the A/D unit 303 on the basis ofa control signal from the symbol timing detector 309, and outputs theremaining signal to the FFT unit 313. The FFT unit 313 performs fastFourier transform on the signal received from the GI remover 311,performs demodulation in the DFT-Spread-OFDM scheme, and outputs thesignal to the subcarrier demapping unit 315. The number of points of theFFT unit 313 is equal to the number of points of an IFFT unit in themobile station apparatus 5 described below.

The subcarrier demapping unit 315 demaps the signal demodulated by theFFT unit 313 into a DM RS, an SRS, a PUSCH signal, and a PUCCH signal onthe basis of a control signal received from the controller 105. Thesubcarrier demapping unit 315 outputs the DM RS resulting from thedemapping to the channel estimator 317, outputs the SRS resulting fromthe demapping to the SRS processor 333, outputs the PUSCH signalresulting from the demapping to the PUSCH channel equalizer 319, andoutputs the PUCCH signal resulting from the demapping to the PUCCHchannel equalizer 321.

The channel estimator 317 estimates channel variations by using the DMRS resulting from the demapping in the subcarrier demapping unit 315 anda known signal. The channel estimator 317 outputs a channel estimationvalue to the PUSCH channel equalizer 319 and the PUCCH channel equalizer321. The PUSCH channel equalizer 319 equalizes the amplitude and phaseof the PUSCH signal resulting from the demapping in the subcarrierdemapping unit 315 on the basis of the channel estimation value receivedfrom the channel estimator 317. Here, equalization means a process ofrestoring channel variations experienced by a signal during radiocommunication. The PUSCH channel equalizer 319 outputs the adjustedsignal to the IDFT unit 323.

The IDFT unit 323 performs inverse discrete Fourier transform on thesignal received from the PUSCH channel equalizer 319 and outputs thesignal to the data demodulator 325. The data demodulator 325 demodulatesthe PUSCH signal subjected to the transform in the IDFT unit 323, andoutputs the demodulated PUSCH signal to the turbo decoder 327. Thedemodulation here corresponds to the modulation scheme used in a datamodulator of the mobile station apparatus 5, and the modulation schemeis received from the controller 105. The turbo decoder 327 decodesinformation data from the PUSCH signal that is demodulated by andreceived from the data demodulator 325. The coding rate is received fromthe controller 105.

The PUCCH channel equalizer 321 equalizes the amplitude and phase of thePUCCH signal resulting from the demapping in the subcarrier demappingunit 315 on the basis of the channel estimation value received from thechannel estimator 317. The PUCCH channel equalizer 321 outputs theequalized signal to the physical uplink control channel detector 329.

The physical uplink control channel detector 329 demodulates and decodesthe signal received from the PUCCH channel equalizer 321, and detectsUCI. The physical uplink control channel detector 329 performs a processof demultiplexing a signal subjected to code multiplexing in thefrequency domain and/or the time domain. The physical uplink controlchannel detector 329 performs a process of detecting an ACK/NACK, an SR,and a CQI from the PUCCH signal subjected to code multiplexing in thefrequency domain and/or the time domain by using a code sequence used onthe transmission side. Specifically, as a detection process using a codesequence in the frequency domain, that is, as a process ofdemultiplexing a signal subjected to code multiplexing in the frequencydomain, the physical uplink control channel detector 329 multiplies thesignal for each subcarrier of the PUCCH by each code in the codesequence, and then combines the signals resulting from multiplication byeach code. Specifically, as a detection process using a code sequence inthe time domain, that is, as a process of demultiplexing the signalsubjected to code multiplexing in the time domain, the physical uplinkcontrol channel detector 329 multiplies a signal for each SC-FDMA symbolof PUCCH by each code in the code sequence, and then combines thesignals resulting from multiplication by each code. The physical uplinkcontrol channel detector 329 sets a detection process for the PUCCHsignal on the basis of a control signal from the controller 105.

The SRS processor 333 measures the channel quality by using the SRSreceived from the subcarrier demapping unit 315, and outputs ameasurement result of the channel quality of the UL PRB (UL PRB pair) tothe controller 105. The SRS processor 333 receives, from the controller105, an instruction indicating the uplink subframe and the UL PRB (ULPRB pair) for which the measurement of channel quality of the mobilestation apparatus 5 is to be performed for the signal. Also, the SRSprocessor 333 detects an out-of-synchronization state on the uplink byusing the SRS received from the subcarrier demapping unit 315, andoutputs information representing the out-of-synchronization state on theuplink (out-of-synchronization information) to the controller 105. TheSRS processor 333 may perform a process of detecting anout-of-synchronization state on the uplink from a receive signal in thetime domain. Specifically, the SRS processor 333 may perform a processequivalent to the process performed in the preamble detector 331described below.

The preamble detector 331 performs a process of detecting (receiving) apreamble transmitted for a receive signal corresponding to the PRACH onthe basis of a signal received from the A/D unit 303. Specifically, thepreamble detector 331 performs a correlation process between a replicasignal that is possibly transmitted and is generated by using eachpreamble sequence, and receive signals at various timings in guard time.For example, if a correlation value is higher than a preset threshold,the preamble detector 331 determines that the same signal as thepreamble sequence used to generate the replica signal used in thecorrelation process has been transmitted from the mobile stationapparatus 5. The preamble detector 331 determines the timing with thehighest correlation value to be arrival timing of the preamble sequence.The preamble detector 331 generates preamble detection information atleast including information indicating the detected preamble sequenceand information indicating the arrival timing, and outputs the preambledetection information to the controller 105.

The controller 105 controls the subcarrier demapping unit 315, the datademodulator 325, the turbo decoder 327, the channel estimator 317, andthe physical uplink control channel detector 329 on the basis of controlinformation (DCI) transmitted from the base station apparatus 3 to themobile station apparatus 5 by using the PDCCH and control information(RRC signaling) transmitted from the base station apparatus 3 to themobile station apparatus 5 by using the PDSCH. Also, the controller 105grasps the resources (uplink subframe, UL PRB (UL PRB pair), codesequence in the frequency domain, code sequence in the time domain)constituting the PRACH, PUSCH, PUCCH, and SRS that have been transmitted(may have been transmitted) from each mobile station apparatus 5, on thebasis of the control information transmitted from the base stationapparatus 3 to the mobile station apparatus 5.

<Overall Configuration of Mobile Station Apparatus 5>

The configuration of the mobile station apparatus 5 according to theembodiment will be described below with reference to FIGS. 4, 5, and 6.FIG. 4 is a schematic block diagram illustrating the configuration ofthe mobile station apparatus 5 according to the embodiment of thepresent invention. As illustrated in FIG. 4, the mobile stationapparatus 5 includes a reception processor (first reception processor)401, a radio resource controller (first radio resource controller) 403,a controller (first controller) 405, and a transmission processor (firsttransmission processor) 407.

The reception processor 401 receives a signal from the base stationapparatus 3, and demodulates and decodes the received signal in responseto an instruction from the controller 405. In the case of detecting asignal on a PDCCH (first PDCCH, second PDCCH) for the mobile stationapparatus 5, the reception processor 401 outputs DCI obtained bydecoding the signal on the PDCCH to the controller 405. For example, thereception processor 401 performs a process of detecting a second PDCCHfor the mobile station apparatus 5 in the search space in the secondPDCCH region specified by the base station apparatus 3. For example, thereception processor 401 sets a search space for candidates of the E-CCEaggregation number, and performs a process of detecting the second PDCCHfor the mobile station apparatus 5. For example, the reception processor401 performs a process of estimating a channel by using a UE-specific RSin the second PDCCH region specified by the base station apparatus 3,demodulating a signal on the second PDCCH, and detecting a signalincluding control information for the mobile station apparatus 5. Forexample, the reception processor 401 performs a process of identifyingtransmit antennas (antenna ports) corresponding to UE-specific RSs usedto demodulate signals on individual E-CCEs in a DL PRB pair in thesecond PDCCH region on the basis of a combination of individual E-CCEsin the DL PRB pair in the second PDCCH region and corresponding antennaports reported from the base station apparatus 3, and detecting a signalincluding control information addressed to the mobile station apparatus5.

Also, the reception processor 401 outputs information data that has beenobtained by decoding the PDSCH for the mobile station apparatus 5 to ahigher layer via the controller 405 in response to an instruction fromthe controller 405 after the DCI included in the PDCCH has been outputto the controller 405. A downlink assignment in the DCI included in thePDCCH includes information representing the assignment of resources ofthe PDSCH. Also, the reception processor 401 outputs the controlinformation that is obtained by decoding the PDSCH and generated by theradio resource controller 103 of the base station apparatus 3 to thecontroller 405, and also to the radio resource controller 403 of themobile station apparatus 5 via the controller 405. For example, thecontrol information generated by the radio resource controller 103 ofthe base station apparatus 3 includes information representing a DL PRBpair in a second PDCCH region, information representing the physicalresource mapping in the second PDCCH region (information representingfirst physical resource mapping or second physical resource mapping),and information representing a combination of individual E-CCEs in theDL PRB pair and corresponding antenna ports (first combination, secondcombination, third combination, or fourth combination).

Further, the reception processor 401 outputs a cyclic redundancy check(CRC) code included in the PDSCH to the controller 405. The transmissionprocessor 107 of the base station apparatus 3 generates a CRC code frominformation data and transmits the information data and the CRC code onthe PDSCH, although this is omitted in the description of the basestation apparatus 3. The CRC code is used to determine whether or notthe data included in the PDSCH is wrong. For example, in a case wherethe information generated from data by using a predetermined generatorpolynomial in the mobile station apparatus 5 is the same as the CRC codethat is generated in the base station apparatus 3 and transmitted on thePDSCH, it is determined that the data is not wrong. In a case where theinformation generated from data by using the predetermined generatorpolynomial in the mobile station apparatus 5 is different from the CRCcode that is generated in the base station apparatus 3 and transmittedon the PDSCH, it is determined that the data is wrong.

Also, the reception processor 401 measures the downlink receptionquality (RSRP: Reference Signal Received Power) and outputs ameasurement result to the controller 405. The reception processor 401measures (calculates) the RSRP from the CRS or CSI-RS in response to aninstruction from the controller 405. The reception processor 401 will bedescribed in detail below.

The controller 405 checks the data that is transmitted from the basestation apparatus 3 using the PDCCH and is received from the receptionprocessor 401, outputs information data in the data to a higher layer,and controls the reception processor 401 and the transmission processor407 on the basis of control information that is included in the data andis generated by the radio resource controller 103 of the base stationapparatus 3. Also, the controller 405 controls the reception processor401 and the transmission processor 407 in response to an instructionfrom the radio resource controller 403. For example, the controller 405controls the reception processor 401 to perform a process of detecting asecond PDCCH on a signal in a DL PRB pair in the second PDCCH regionspecified by the radio resource controller 403. For example, thecontroller 405 controls the reception processor 401 so as to performdemapping of physical resources in the second PDCCH region on the basisof information representing the physical resource mapping in the secondPDCCH region specified by the radio resource controller 403. Here,demapping of physical resources in the second PDCCH region means, forexample, as illustrated in FIGS. 21 and 22, a process of configuring(forming, constructing, creating) second PDCCH candidates for performinga detection process from a signal in the second PDCCH region. Also, thecontroller 405 controls, for the reception processor 401, a region inwhich a process of detecting a second PDCCH in the second PDCCH regionis performed. Specifically, for each second PDCCH region, the controller405 indicates (sets), to the reception processor 401, an E-CCEaggregation number for which a search space is set, the number of thefirst E-CCE in which a process of detecting a second PDCCH in the secondPDCCH region is performed, and the number of second PDCCH candidates,for each E-CCE aggregation number. Also, the controller 405 controls thereception processor 401 so as to use the UE-specific RSs for thetransmit antennas (antenna ports) corresponding to demodulation ofsignals on individual E-CCEs, on the basis of a combination ofindividual E-CCEs in the DL PRB pair and corresponding antenna portsspecified by the radio resource controller 403 (the correspondencebetween individual E-CCEs in the DL PRB pair and corresponding transmitantennas for UE-specific RSs).

Further, the controller 405 controls the reception processor 401 and thetransmission processor 407 on the basis of DCI that is transmitted fromthe base station apparatus 3 using the PDCCH and is received from thereception processor 401. Specifically, the controller 405 controls thereception processor 401 mainly on the basis of a detected downlinkassignment, and controls the transmission processor 407 mainly on thebasis of a detected uplink grant. Also, the controller 405 controls thetransmission processor 407 on the basis of control informationrepresenting a transmit power control command of the PUCCH included inthe downlink assignment. The controller 405 compares the informationgenerated using a predetermined generator polynomial from the datareceived from the reception processor 401 with the CRC code receivedfrom the reception processor 401, determines whether or not the data iswrong, and generates an ACK/NACK. Also, the controller 405 generates anSR and a CQI in response to an instruction from the radio resourcecontroller 403. Also, the controller 405 controls the transmissiontiming of a signal from the transmission processor 407 on the basis ofan adjustment value or the like of the transmission timing on the uplinkreported from the base station apparatus 3. Also, the controller 405controls the transmission processor 407 to transmit informationrepresenting the reception quality (RSRP) of the downlink received fromthe reception processor 401. The base station apparatus 3 may set, forthe mobile station apparatus 5, candidates of an E-CCE aggregationnumber on the basis of the reception quality (RSRP) on the downlinkreported from the mobile station apparatus 5, although this is omittedin the description of the base station apparatus 3. For example, thebase station apparatus 3 may set, for the mobile station apparatus 5having good reception quality in the downlink (the mobile stationapparatus near the center of the cell), E-CCE aggregation 1, E-CCEaggregation 2, and E-CCE aggregation 4 as candidates of an E-CCEaggregation number of Localized E-PDCCH. For example, the base stationapparatus 3 may set, for the mobile station apparatus 5 havingunfavorable reception quality in the downlink (the mobile stationapparatus near the edge of the cell), E-CCE aggregation 2 and E-CCEaggregation 4 as candidates of an E-CCE aggregation number of LocalizedE-PDCCH.

The radio resource controller 403 stores and holds the controlinformation generated by the radio resource controller 103 of the basestation apparatus 3 and reported from the base station apparatus 3, andcontrols the reception processor 401 and the transmission processor 407via the controller 405. That is, the radio resource controller 403 has afunction of a memory for holding various parameters and the like. Forexample, the radio resource controller 403 holds information regarding aDL PRB pair in the second PDCCH region, information regarding thephysical resource mapping in the second PDCCH region, and informationregarding a combination of individual E-CCEs in the DL PRB pair in thesecond PDCCH region and corresponding antenna ports (first combination,second combination, third combination, or fourth combination), andoutputs various control signals to the controller 405. The radioresource controller 403 holds parameters related to transmit powers ofthe PUSCH, PUCCH, SRS, and PRACH, and outputs a control signal to thecontroller 405 so that the parameters reported from the base stationapparatus 3 are used.

The radio resource controller 403 sets values of parameters related tothe transmit powers of the PUCCH, PUSCH, SRS, PRACH, and so forth. Thevalues of the transmit powers set by the radio resource controller 403are output to the transmission processor 407 by the controller 405. Fora DM RS constituted by the resource in the same UL PRB as the PUCCH, thesame transmit power control as that for the PUCCH is performed. For a DMRS constituted by the resource in the same UL PRB as the PUSCH, the sametransmit power control as that for the PUSCH is performed. The radioresource controller 403 sets, for the PUSCH, the values of a parameterbased on the number of UL PRB pairs assigned to the PUSCH, a parameterspecific to a cell reported in advance from the base station apparatus3, a parameter specific to a mobile station apparatus reported inadvance from the base station apparatus 3, a parameter based on themodulation scheme used for the PUSCH, a parameter based on the value ofestimated path loss, a parameter based on a transmit power controlcommand reported from the base station apparatus 3, and so forth. Theradio resource controller 403 sets, for the PUCCH, the values of aparameter based on the signal configuration of the PUCCH, a parameterspecific to a cell reported in advance from the base station apparatus3, a parameter specific to a mobile station apparatus reported inadvance from the base station apparatus 3, a parameter based on thevalue of estimated path loss, a parameter based on a reported transmitpower control command, and so forth.

As a parameter related to transmit power, a parameter specific to a celland a parameter specific to a mobile station apparatus are reported fromthe base station apparatus 3 using the PDSCH, and a transmit powercontrol command is reported from the base station apparatus 3 using thePDCCH. The transmit power control command for the PUSCH is included inan uplink grant, and the transmit power control command for the PUCCH isincluded in a downlink assignment. The various parameters that arerelated to transmit powers and that are reported from the base stationapparatus 3 are appropriately stored in the radio resource controller403, and the stored values are input to the controller 405.

The transmission processor 407 transmits a signal that is obtained byencoding and modulating information data and UCI to the base stationapparatus 3 via a transmit antenna 411 by using the resources of thePUSCH and PUCCH in response to an instruction from the controller 405.Also, the transmission processor 407 sets the transmit powers of thePUSCH, PUCCH, SRS, DM RS, and PRACH in response to an instruction fromthe controller 405. The transmission processor 407 will be described indetail below.

<Reception Processor 401 of Mobile Station Apparatus 5>

Hereinafter, the reception processor 401 of the mobile station apparatus5 will be described in detail. FIG. 5 is a schematic block diagramillustrating the configuration of the reception processor 401 of themobile station apparatus 5 according to the embodiment of the presentinvention. As illustrated in FIG. 5, the reception processor 401includes a reception RF unit 501, an A/D unit 503, a symbol timingdetector 505, a GI remover 507, an FFT unit 509, a demultiplexer 511, achannel estimator 513, a PDSCH channel compensator 515, a physicaldownlink shared channel decoder 517, a PDCCH channel compensator 519, aphysical downlink control channel decoder 521, a downlink receptionquality measurement unit 531, and a PDCCH demapping unit 533. Also, asillustrated in FIG. 5, the physical downlink shared channel decoder 517includes a data demodulator 523 and a turbo decoder 525. Also, asillustrated in FIG. 5, the physical downlink control channel decoder 521includes a QPSK demodulator 527 and a Viterbi decoder 529.

The reception RF unit 501 appropriately amplifies a signal received bythe receive antenna 409, converts (down-converts) the signal into anintermediate frequency, removes unnecessary frequency components,controls the amplification level so that the signal level isappropriately kept, and performs orthogonal demodulation on the basis ofthe in-phase components and orthogonal components of the receivedsignal. The reception RF unit 501 outputs the analog signal subjected toorthogonal demodulation to the A/D unit 503.

The A/D unit 503 converts the analog signal subjected to the orthogonaldemodulation in the reception RF unit 501 into a digital signal, andoutputs the digital signal resulting from the conversion to the symboltiming detector 505 and the GI remover 507. The symbol timing detector505 detects the timing of a symbol on the basis of the digital signalobtained from the A/D unit 503, and outputs a control signalrepresenting the detected timing of a symbol boundary to the GI remover507. The GI remover 507 removes a part corresponding to guard intervalfrom the digital signal output from the A/D unit 503 on the basis of thecontrol signal from the symbol timing detector 505, and outputs theremaining signal to the FFT unit 509. The FFT unit 509 performs fastFourier transform on the signal received from the GI remover 507,performs demodulation in the OFDM scheme, and outputs the signal to thedemultiplexer 511.

The demultiplexer 511 demultiplexes the signal demodulated by the FFTunit 509 into a signal of the PDCCH (first PDCCH, second PDCCH) and asignal of the PDSCH on the basis of a control signal received from thecontroller 405. The demultiplexer 511 outputs the signal of the PDSCHobtained through demultiplexing to the PDSCH channel compensator 515,and outputs the signal of the PDCCH obtained through demultiplexing tothe PDCCH channel compensator 519. For example, the demultiplexer 511outputs a signal on the second PDCCH in the second PDCCH regionspecified for the mobile station apparatus 5 to the PDCCH channelcompensator 519. Also, the demultiplexer 511 demultiplexes the downlinkresource elements to which downlink reference signals are mapped, andoutputs the downlink reference signals (CRS, UE-specific RS) to thechannel estimator 513. For example, the demultiplexer 511 outputs theUE-specific RS in the second PDCCH region specified for the mobilestation apparatus 5 to the channel estimator 513. Also, thedemultiplexer 511 outputs downlink reference signals (CRS, CSI-RS) tothe downlink reception quality measurement unit 531.

The channel estimator 513 estimates channel variations by using thedownlink reference signals obtained through demultiplexing performed bythe demultiplexer 511 and a known signal, and outputs a channelcompensation value for adjusting the amplitude and phase to the PDSCHchannel compensator 515 and the PDCCH channel compensator 519 so as tocompensate for channel variations. The channel estimator 513independently estimates channel variations by using the CRS and theUE-specific RS, and outputs a channel compensation value. For example,the channel estimator 513 generates a channel compensation value from achannel estimation value estimated by using the UE-specific RSs mappedto a plurality of DL PRB pairs in the second PDCCH region specified forthe mobile station apparatus 5, and outputs the channel compensationvalue to the PDCCH channel compensator 519. The channel estimator 513performs channel estimation and generates a channel compensation valueby using the UE-specific RSs for the individual transmit antennas(antenna ports) specified by the controller 405. For example, thechannel estimator 513 generates a channel compensation value from achannel estimation value estimated by using the UE-specific RSs mappedto the plurality of DL PRB pairs assigned to the mobile stationapparatus 5 and assigned to the PDSCH, and outputs the channelcompensation value to the PDSCH channel compensator 515. For example,the channel estimator 513 generates a channel compensation value from achannel estimation value estimated by using a CRS, and outputs thechannel compensation value to the PDCCH channel compensator 519. Forexample, the channel estimator 513 generates a channel compensationvalue from a channel estimation value estimated by using a CRS, andoutputs the channel compensation value to the PDSCH channel compensator515.

The PDSCH channel compensator 515 adjusts the amplitude and phase of thesignal of the PDSCH obtained through demultiplexing performed by thedemultiplexer 511 on the basis of the channel compensation valuereceived from the channel estimator 513. For example, the PDSCH channelcompensator 515 performs adjustment on a signal on a certain PDSCH onthe basis of a channel compensation value generated by the channelestimator 513 on the basis of a UE-specific RS, and performs adjustmenton a signal on another PDSCH on the basis of a channel compensationvalue generated by the channel estimator 513 on the basis of a CRS. ThePDSCH channel compensator 515 outputs the signal for which the channelhas been adjusted to the data demodulator 523 of the physical downlinkshared channel decoder 517.

The physical downlink shared channel decoder 517 demodulates and decodesthe PDSCH in response to an instruction from the controller 405, anddetects information data. The data demodulator 523 demodulates thesignal on the PDSCH received from the channel compensator 515, andoutputs the demodulated signal on the PDSCH to the turbo decoder 525.The demodulation performed here is demodulation corresponding to themodulation scheme used in the data modulator 221 of the base stationapparatus 3. The turbo decoder 525 decodes information data from thedemodulated signal on the PDSCH received from the data demodulator 523,and outputs the information data to a higher layer via the controller405. The control information and so forth that is transmitted using thePDSCH and that is generated by the radio resource controller 103 of thebase station apparatus 3 is also output to the controller 405, and isalso output to the radio resource controller 403 via the controller 405.The CRC code included in the PDSCH is also output to the controller 405.

The PDCCH channel compensator 519 adjusts the amplitude and phase of thesignal of the PDCCH obtained through demultiplexing performed by thedemultiplexer 511 on the basis of the channel compensation valuereceived from the channel estimator 513. For example, the PDCCH channelcompensator 519 performs adjustment on a signal on the second PDCCH onthe basis of the channel compensation value generated by the channelestimator 513 on the basis of a UE-specific RS, and performs adjustmenton a signal on the first PDCCH on the basis of the channel compensationvalue generated by the channel estimator 513 on the basis of a CRS. Forexample, the PDCCH channel compensator 519 adjusts the signals onindividual E-CCEs in a DL PRB pair in the second PDCCH region on thebasis of a channel compensation value generated on the basis of theUE-specific RSs for the transmit antennas (antenna ports) correspondingto the individual E-CCEs specified by the controller 405. The PDCCHchannel compensator 519 outputs the adjusted signal to the PDCCHdemapping unit 533.

The PDCCH demapping unit 533 performs demapping for the first PDCCH ordemapping for the second PDCCH on the signal received from the PDCCHchannel compensator 519. Further, the PDCCH demapping unit 533 performsdemapping for the first physical resource mapping or demapping for thesecond physical resource mapping on the signal on the second PDCCHreceived from the PDCCH channel compensator 519. The PDCCH demappingunit 533 converts the received signal on the first PDCCH to a signal inunits of CCEs as described above with reference to FIG. 16 so thatprocessing is performed in units of CCEs illustrated in FIG. 15 on thereceived signal on the first PDCCH in the physical downlink controlchannel decoder 521. The PDCCH demapping unit 533 converts the receivedsignal on the second PDCCH to a signal in units of E-CCEs so thatprocessing is performed in units of E-CCEs illustrated in FIG. 18 on thereceived signal on the second PDCCH in the physical downlink controlchannel decoder 521. The PDCCH demapping unit 533 converts the receivedsignal on the second PDCCH in the second PDCCH region to which the firstphysical resource mapping is applied to a signal in units of E-CCEs, asdescribed above with reference to FIG. 21. The PDCCH demapping unit 533converts the received signal on the second PDCCH in the second PDCCHregion to which the second physical resource mapping is applied to asignal in units of E-CCEs, as described above with reference to FIG. 22.The PDCCH demapping unit 533 outputs the converted signal to the QPSKdemodulator 527 of the physical downlink control channel decoder 521.

The physical downlink control channel decoder 521 demodulates anddecodes the signal received from the PDCCH channel compensator 519 anddetects control data as described below. The QPSK demodulator 527performs QPSK demodulation on the signal on the PDCCH and outputs thesignal to the Viterbi decoder 529. The Viterbi decoder 529 decodes thesignal demodulated by the QPSK demodulator 527 and outputs DCI obtainedthrough decoding to the controller 405. Here, this signal is expressedin units of bits, and the Viterbi decoder 529 also performs ratedematching to adjust the number of bits on which Viterbi decodingprocessing is to be performed for input bits.

First, a description will be given of a detection process for the firstPDCCH. The mobile station apparatus 5 performs a process of detectingDCI addressed to the mobile station apparatus 5 under the assumption ofa plurality of CCE aggregation numbers. The mobile station apparatus 5performs a decoding process that differs every assumed CCE aggregationnumber (coding rate) on the signal on the first PDCCH, and obtains DCIincluded in the first PDCCH in which no error is detected in a CRC codeadded to the first PDCCH together with the DCI. Such a process isreferred to as blind decoding. The mobile station apparatus 5 does notperform blind decoding on the signals (receive signals) of all the CCEs(REGs) in the downlink system band under the assumption of the firstPDCCH, but performs blind decoding on only some of the CCEs. Some of theCCEs on which blind decoding is performed are referred to as a searchspace (search space for the first PDCCH). Further, different searchspaces (search spaces for the first PDCCH) are defined for individualCCE aggregation numbers. In the communication system 1 according to theembodiment of the present invention, different search spaces (searchspaces for the first PDCCH) are set for the first PDCCH in the mobilestation apparatus 5. Here, the search spaces for the first PDCCHs of theindividual mobile station apparatuses 5 (search spaces for the firstPDCCHs) may be made up of CCEs totally different from one another, ormay be made up of CCEs totally identical to one another, or may be madeup of CCEs that partially overlap with one another.

Next, a description will be given of a detection process for the secondPDCCH. The mobile station apparatus 5 performs a process of detectingDCI for the mobile station apparatus 5 under the assumption of aplurality of E-CCE aggregation numbers. The mobile station apparatus 5performs a decoding process that differs every assumed E-CCE aggregationnumber (coding rate) on the signal on the second PDCCH, and obtains DCIincluded in the second PDCCH in which no error is detected in the CRCcode added to the second PDCCH together with the DCI. Such a process isreferred to as blind decoding. The mobile station apparatus 5 does notperform blind decoding on the signals (receive signals) on all theE-CCEs in the second PDCCH region configured by the base stationapparatus 3 under the assumption of the second PDCCH, but may performblind decoding on only some of the E-CCEs. Some of the E-CCEs on whichblind decoding is performed are referred to as a search space (searchspace for the second PDCCH). Different search spaces (search spaces forthe second PDCCH) are defined for the individual E-CCE aggregationnumbers. For the mobile station apparatus 5 for which a plurality ofsecond PDCCH regions are configured, a search space is set (configured,defined) to each of the second PDCCH regions. For the mobile stationapparatus 5, a search space is set for each of the second PDCCH regionto which the first physical resource mapping is applied and the secondPDCCH region to which the second physical resource mapping is applied.For the mobile station apparatus 5 for which a plurality of second PDCCHregions are configured, a plurality of search spaces are simultaneouslyset in a certain downlink subframe.

In the communication system 1 according to the embodiment of the presentinvention, different search spaces (search spaces for the second PDCCH)are set for the second PDCCH in the mobile station apparatus 5. Here,the search spaces for the second PDCCHs of the individual mobile stationapparatuses 5 for which the same second PDCCH region is configured(search spaces for the second PDCCHs) may be made up of E-CCEs totallydifferent from one another, or may be made up E-CCEs totally identicalto one another, or may be made up of E-CCEs that partially overlap withone another.

For the mobile station apparatus 5 for which a plurality of second PDCCHregions are configured, a search space (search space for the secondPDCCH) is set in each second PDCCH region. A search space (search spacefor the second PDCCH) means a logical region in which the mobile stationapparatus 5 performs decoding and detection of the second PDCCH in thesecond PDCCH region. The search space (search space for the secondPDCCH) is made up of a plurality of second PDCCH candidates. The secondPDCCH candidates are targets on which the mobile station apparatus 5performs decoding and detection of the second PDCCH. For each E-CCEaggregation number, different second PDCCH candidates are made up ofdifferent E-CCEs (including one E-CCE and a plurality of E-CCEs). TheE-CCEs constituting a plurality of second PDCCH candidates of the searchspace (search space for the second PDCCH) in the second PDCCH region towhich the first physical resource mapping is applied are made up of aplurality of E-CCEs in contiguous regions. The first E-CCE number thatis used for the search space (search space for the second PDCCH) in thesecond PDCCH region is set for each mobile station apparatus 5. TheE-CCEs constituting a plurality of second PDCCH candidates of the searchspace (search space for the second PDCCH) in the second PDCCH region towhich the second physical resource mapping is applied are made up of aplurality of noncontiguous regions. The first E-CCE number that is usedfor the search space (search space for the second PDCCH) in the secondPDCCH region is set for each mobile station apparatus 5 in each secondPDCCH region. For example, with a random function using an identifier(mobile station identifier) assigned to the mobile station apparatus 5,the first E-CCE number that is used for the search space (search spacefor the second PDCCH) is set. For example, the base station apparatus 3notifies the mobile station apparatus 5 of the first E-CCE number thatis used in the search space (search space for the second PDCCH) by usingRRC signaling.

The number of second PDCCH candidates may be different among theindividual search spaces (search spaces for the second PDCCH) in aplurality of second PDCCH regions. The number of second PDCCH candidatesin the search space (search space for the second PDCCH) in the secondPDCCH region to which the first physical resource mapping is applied maybe larger than the number of second PDCCH candidates in the search space(search space for the second PDCCH) in the second PDCCH region to whichthe second physical resource mapping is applied.

In a certain E-CCE aggregation number, the number of second PDCCHcandidates in the search space (search space for the second PDCCH) inthe second PDCCH region to which the first physical resource mapping isapplied may be the same as the number of second PDCCH candidates in thesearch space (search space for the second PDCCH) in the second PDCCHregion to which the second physical resource mapping is applied. In adifferent E-CCE aggregation number, the number of second PDCCHcandidates in the search space (search space for the second PDCCH) inthe second PDCCH region to which the first physical resource mapping isapplied may be different from the number of second PDCCH candidates inthe search space (search space for the second PDCCH) in the second PDCCHregion to which the second physical resource mapping is applied.

The second PDCCH candidates of a certain E-CCE aggregation number may beconfigured for the search space (search space for the second PDCCH) inone second PDCCH region, and may not be configured for the search space(search space for the second PDCCH) in another second PDCCH region.

The number of second PDCCH candidates in the search space (search spacefor the second PDCCH) in one second PDCCH region may be changed on thebasis of the number of second PDCCH regions configured for the mobilestation apparatus 5. For example, as the number of second PDCCH regionsconfigured for the mobile station apparatus 5 increases, the number ofsecond PDCCH candidates in the search space (search space for the secondPDCCH) in one second PDCCH region may be decreased.

The mobile station apparatus 5 configures the search space correspondingto the candidates of the E-CCE aggregation number to the second PDCCHregion to which the first physical resource mapping is applied. Themobile station apparatus 5 identifies the transmit antennas (antennaports) to be used for transmitting signals on individual E-CCEs in a DLPRB pair in the second PDCCH region on the basis of a combination ofindividual E-CCEs in the DL PRB pair and corresponding antenna portsreported from the base station apparatus 3 (the correspondence betweenthe individual E-CCEs in the DL PRB pair in the second PDCCH region andantenna ports (transmit antenna) corresponding to the individualE-CCEs).

The controller 405 determines whether the DCI received from the Viterbidecoder 529 is correct DCI for the mobile station apparatus 5. In thecase of determining that the DCI is correct DCI for the mobile stationapparatus 5, the controller 405 controls the demultiplexer 511, the datademodulator 523, the turbo decoder 525, and the transmission processor407 on the basis of the DCI. For example, in a case where the DCI is adownlink assignment, the controller 405 controls the reception processor401 to decode the signal on the PDSCH. In the PDCCH, as in the PDSCH, aCRC code is included, and the controller 405 determines whether or notthe DCI of the PDCCH is wrong by using the CRC code.

The downlink reception quality measurement unit 531 measures thereception quality (RSRP) in the downlink of the cell by using downlinkreference signals (CRS, CSI-RS), and outputs downlink reception qualityinformation obtained through the measurement to the controller 405.Also, the downlink reception quality measurement unit 531 measuresinstantaneous channel quality for generating a CQI to be reported fromthe mobile station apparatus 5 to the base station apparatus 3. Thedownlink reception quality measurement unit 531 outputs information onRSRP and so forth obtained through the measurement to the controller405.

<Transmission Processor 407 of Mobile Station Apparatus 5>

FIG. 6 is a schematic block diagram illustrating the configuration ofthe transmission processor 407 of the mobile station apparatus 5according to the embodiment of the present invention. As illustrated inFIG. 6, the transmission processor 407 includes a turbo encoder 611, adata modulator 613, a DFT unit 615, an uplink pilot channel processor617, a physical uplink control channel processor 619, a subcarriermapping unit 621, an IFFT unit 623, a GI insertion unit 625, a transmitpower adjuster 627, a random access channel processor 629, a D/A unit605, a transmission RF unit 607, and the transmit antenna 411. Thetransmission processor 407 encodes and modulates information data andUCI, generates signals to be transmitted using the PUSCH and PUCCH, andadjusts the transmit power of the PUSCH and PUCCH. The transmissionprocessor 407 generates a signal to be transmitted using the PRACH, andadjusts the transmit power of the PRACH. The transmission processor 407generates a DM RS and an SRS, and adjusts the transmit power of the DMRS and the SRS.

The turbo encoder 611 performs, on information data input thereto, turbocoding to enhance the error resilience of the data at a coding ratespecified by the controller 405, and outputs the information data to thedata modulator 613. The data modulator 613 modulates the encoded dataobtained through encoding performed by the turbo encoder 611 by using amodulation scheme specified by the controller 405, for example, amodulation scheme such as QPSK, 16QAM, and 64QAM, and generates a signalsequence of modulation symbols. The data modulator 613 outputs thegenerated signal sequence of modulation symbols to the DFT unit 615. TheDFT unit 615 performs discrete Fourier transform on the signal outputfrom the data modulator 613, and outputs the signal to the subcarriermapping unit 621.

The physical uplink control channel processor 619 performs basebandsignal processing for transmitting the UCI received from the controller405. The UCI input to the physical uplink control channel processor 619is an ACK/NACK, an SR, or a CQI. The physical uplink control channelprocessor 619 performs baseband signal processing, and outputs a signalgenerated thereby to the subcarrier mapping unit 621. The physicaluplink control channel processor 619 encodes the information bits of theUCI to generate a signal.

Also, the physical uplink control channel processor 619 performs signalprocessing relating to code multiplexing in the frequency domain and/orcode multiplexing in the time domain on the signal generated from theUCI. The physical uplink control channel processor 619 multiplies asignal on the PUCCH generated from the information bit of an ACK/NACK,or the information bit of an SR, or the information bit of a CQI, by acode sequence specified by the controller 405 in order to realize codemultiplexing in the frequency domain. The physical uplink controlchannel processor 619 multiplies a signal on the PUCCH generated fromthe information bit of an ACK/NACK, or the information bit of an SR, bya code sequence specified by the controller 405 in order to realize codemultiplexing in the time domain.

The uplink pilot channel processor 617 generates an SRS and a DM RS,which are known signals in the base station apparatus 3, in response toan instruction from the controller 405, and outputs them to thesubcarrier mapping unit 621.

The subcarrier mapping unit 621 maps the signal received from the uplinkpilot channel processor 617, the signal received from the DFT unit 615,and the signal received from the physical uplink control channelprocessor 619 to a subcarrier in response to an instruction from thecontroller 405, and outputs the signals to the IFFT unit 623.

The IFFT unit 623 performs inverse fast Fourier transform on the signalsoutput from the subcarrier mapping unit 621, and outputs the signals tothe GI insertion unit 625. Here, the number of points of the IFFT unit623 is larger than the number of points of the DFT unit 615. The mobilestation apparatus 5 modulates, using the DFT-Spread-OFDM scheme, on thesignal to be transmitted using the PUSCH, by using the DFT unit 615, thesubcarrier mapping unit 621, and the IFFT unit 623. The GI insertionunit 625 adds guard interval to the signals received from the IFFT unit623, and outputs the signals to the transmit power adjuster 627.

The random access channel processor 629 generates a signal to betransmitted using the PRACH by using a preamble sequence specified bythe controller 405, and outputs the generated signal to the transmitpower adjuster 627.

The transmit power adjuster 627 adjusts the transmit power of the signalreceived from the GI insertion unit 625 or the signal received from therandom access channel processor 629 on the basis of a control signalfrom the controller 405, and outputs the signal to the D/A unit 605. Inthe transmit power adjuster 627, the average transmit powers of thePUSCH, PUCCH, DMRS, SRS, and PRACH are controlled for each uplinksubframe.

The D/A unit 605 converts the baseband digital signal received from thetransmit power adjuster 627 to an analog signal, and outputs the analogsignal to the transmission RF unit 607. The transmission RF unit 607generates in-phase components and orthogonal components of anintermediate frequency from the analog signal received from the D/A unit605, and removes extra frequency components for the intermediatefrequency band. Subsequently, the transmission RF unit 607 converts(up-converts) the intermediate-frequency signal into a high-frequencysignal, removes extra frequency components, amplifies the power, andtransmits the signal to the base station apparatus 3 via the transmitantenna 411.

FIG. 7 is a flowchart illustrating an example of a process related toconfiguration of a UE-specific RS used to demodulate individual E-CCEsin the DL PRB pair in the second PDCCH region, performed by the mobilestation apparatus 5 according to the embodiment of the presentinvention. Here, a description will be given of an example of a processperformed in the second PDCCH region to which the first physicalresource mapping is applied.

The mobile station apparatus 5 receives, from the base station apparatus3, information representing a combination of individual E-CCEs in the DLPRB pair and corresponding antenna ports by using RRC signaling (stepS101). Subsequently, on the basis of the information received from thebase station apparatus 3, the mobile station apparatus 5 performsconfiguration to demodulate the signals on the individual E-CCEs in theDL PRB pair by using UE-specific RSs of the corresponding antenna ports(step S102).

FIG. 8 is a flowchart illustrating an example of a process related toconfiguration of transmit antennas (antenna ports) to be used totransmit individual E-CCEs in the DL PRB pair in the second PDCCHregion, performed by the base station apparatus 3 according to theembodiment of the present invention. Here, a description will be givenof an example of a process performed in the second PDCCH region to whichthe first physical resource mapping is applied.

The base station apparatus 3 sets, for a certain mobile stationapparatus 5, a combination of individual E-CCEs in the DL PRB pair andcorresponding antenna ports, on the basis of the arrangement state ofmobile station apparatuses 5 in the cell (on the basis of adetermination result about application of MU-MIMO) (step T101).Subsequently, the base station apparatus 2 performs configuration totransmit the signals on the individual E-CCEs in the DL PRB pair byusing the corresponding antenna ports (step T102).

A description will be given below of the embodiment from another pointof view. A base station apparatus includes a transmission unit(transmission RF unit) that transmits a signal obtained by frequencymultiplexing a PDSCH (physical shared channel or shared channel) forcarrying data addressed to a terminal apparatus and an E-PDCCH (physicalcontrol channel or control channel) for carrying control informationaddressed to the terminal apparatus by using L resource block pairs (Lis an integer of 2 or more) arranged in the frequency direction within asystem bandwidth; a mapping unit (multiplexer) that maps M E-CCEs (firstelements, control information elements) constituting one E-PDCCH (Mrepresents an E-CCE aggregation number and is a natural number), to anyK resource elements (K is a natural number) in the L×N regions (secondelements) that are obtained by dividing each of the L resource blocksinto N regions (N is a natural number); and a notification unit (radioresource controller) that notifies the terminal apparatus of informationspecifying the N or K and/or information specifying a possible set ofthe M.

On the other hand, the terminal apparatus includes a reception unit(reception RF unit) that receives a signal obtained by frequencymultiplexing a physical shared channel for carrying data addressed tothe terminal apparatus and a physical control channel for carryingcontrol information addressed to the terminal apparatus by using Lresource block pairs (L is an integer of 2 or more) arranged in thefrequency direction within a system bandwidth; a monitoring unit (PDCCHdemapping unit and physical downlink control channel decoder) thatconfigures one physical control channel by combining M (natural number)control information elements mapped to any K resource elements (K is anatural number) in the L×N regions that are obtained by dividing each ofthe L resource blocks into N regions (N is a natural number); and anobtaining unit (radio resource controller) that obtains informationspecifying the N or K and/or information specifying a possible set ofthe M.

Here, for example, N=4 in FIG. 21 (or FIG. 22) and FIG. 23, whereas K=2in FIG. 21 (or FIG. 22), and K=1 in FIG. 23. In this way, in the case ofchanging K by fixing N, the base station apparatus notifies the terminalapparatus of K, and the terminal apparatus obtains K. Accordingly, thenumber of resource elements included in one E-CCE can be limited.Alternatively, N may be changed by fixing K. For example, N is fixed to1, and switching is performed between K=2 and K=1. In a case where N=2and K=1, a resource element is divided into two regions, and one E-CCEis mapped to each of the regions, which is substantially the same as theassignment illustrated in FIG. 21. N=1 and K=1 is illustrated in FIG.23. In this way, in the case of changing N by fixing K, the base stationapparatus notifies the terminal apparatus of N, and the terminalapparatus obtains N. Accordingly, the number of resource elementsincluded in one E-CCE can be limited. FIGS. 21 to 23 illustrate thecases where a resource block pair is divided along the frequency axis,but the embodiment is not limited to these cases. For example, in a casewhere a resource block pair is divided into i regions along thefrequency axis and j regions along the time axis, the resource blockpair is divided into i×j regions along the frequency axis and time axis(i and j are natural numbers).

Alternatively, N and K may be fixed, a possible set of M may be changed,the base station apparatus may notify the terminal apparatus of M, andthe terminal apparatus may obtain M. For example, N=1 and K=1, and apossible set of M (a set of possible values of M) is switched between afirst set {1, 2, 4, 8} and a second set {2, 4, 8, 16}. The terminalperforms blind decoding (attempts configuration and decoding of E-PDCCH)on reported candidates of E-CCE aggregation number. Accordingly, thenumber of resource elements included in one E-PDCCH can be limited.Here, it is preferable that the second set include a value larger thanany values included in the first set (in this case 16). Accordingly, themaximum number of resource elements included in an E-PDCCH can bechanged. Preferably, the first set and the second set include the samenumber of values (in this case 4). Accordingly, the number of candidatesis the same in the first set and the second set, and the number of blinddecoding (the number of attempts of configuration and decoding ofE-PDCCH) is constant.

As described above, in the embodiment of the present invention, in thecommunication system 1, a plurality of physical resource block pairs(PRB pairs) are configured as a control channel region (second PDCCHregion) (second PDCCH region to which first physical resource mapping isapplied), which is a region where a control channel (second PDCCH) ispossibly mapped, a first element (E-CCE) is made up of resourcesobtained by dividing one physical resource block pair (PRB pair), andthe control channel (second PDCCH) is made up of an aggregation of oneor more first elements (E-CCEs) (E-CCE aggregation). The system includesa plurality of mobile station apparatuses 5 and a base station apparatus3 that communicates with the plurality of mobile station apparatuses 5by using a control channel (second PDCCH). The base station apparatus 3sets, for each mobile station apparatus 5, any one of a plurality ofcombinations regarding the correspondence between a plurality of firstelements (E-CCEs) in a physical resource block pair (PRB pair) and aplurality of antenna ports used to transmit the signals on theindividual first elements (E-CCEs). On the basis of the combination setby the base station apparatus 3, the mobile station apparatus 5configures the antenna ports corresponding to reference signals(UE-specific RSs) used to demodulate the signals on the individual firstelements (E-CCEs) in the physical resource block pair (PRB pair).Accordingly, the base station apparatus 3 is capable of efficientlyperforming control to increase the capacity of the entire controlchannel, by increasing the capacity of the entire control channel byperforming spatial multiplexing of the second PDCCH in application ofMU-MIMO and by improving the performance of the second PDCCH inapplication of beamforming, not MU-MIMO.

In the embodiment of the present invention, to simplify the description,the region of resources in which a second PDCCH is possibly mapped isdefined as a second PDCCH region. It is clear that the present inventionis applicable to a region defined by another term as long as the termhas a similar meaning.

The mobile station apparatus 5 is not limited to a mobile terminal, andthe present invention may be realized by installing the function of themobile station apparatus 5 into a fixed terminal.

The characteristic means of the present invention described above canalso be implemented by installing the function in an integrated circuitand controlling the function. That is, an integrated circuit accordingto the present invention is an integrated circuit which is mounted in amobile station apparatus that communicates with a base station apparatusby using a control channel, and for which a plurality of physicalresource block pairs are configured as a control channel region, whichis a region in which the control channel is possibly mapped, firstelements are made up of resources obtained by dividing one of thephysical resource block pairs, and the control channel is made up of anaggregation of one or more first elements. The integrated circuitincludes a first receiver that receives, from the base stationapparatus, information representing any one of a plurality ofcombinations regarding the correspondence between the plurality of firstelements in the physical resource block pair and a plurality of antennaports that are used to transmit signals on the individual firstelements, and a first radio resource controller that configures, on thebasis of the information representing the combination received by thefirst receiver, antenna ports corresponding to the reference signalsused to demodulate the signals on the individual first elements in thephysical resource block pair.

The integrated circuit according to the present invention is anintegrated circuit which is mounted in a base station apparatus thatcommunicates with a plurality of mobile station apparatuses by using acontrol channel, and for which a plurality of physical resource blockpairs are configured as a control channel region, which is a region inwhich the control channel is possibly mapped, first elements are made upof resources obtained by dividing one of the physical resource blockpairs, and the control channel is made up of an aggregation of one ormore first elements. The integrated circuit includes a second radioresource controller that sets, for the mobile station apparatuses, anyone of a plurality of combinations regarding the correspondence betweenthe plurality of first elements in the physical resource block pair anda plurality of antenna ports that are used to transmit signals on theindividual first elements.

The operation described in the embodiment of the present invention maybe implemented by a program. The program that operates in the mobilestation apparatus 5 and the base station apparatus 3 according to thepresent invention is a program that controls a CPU or the like (programthat causes a computer to function) to implement the function of theabove-described embodiment according to the present invention. Theinformation handled in these apparatuses is temporarily stored in a RAMduring processing, and is then stored in various ROMs or HDDs, is readout by the CPU if necessary, and is modified or written. A recordingmedium that stores the program may be any one of a semiconductor medium(for example, a ROM, a nonvolatile memory card, or the like), an opticalrecording medium (for example, a DVD, an MO, an MD, a CD, a BD, or thelike), a magnetic recording medium (for example, a magnetic tape, aflexible disk, or the like), and so forth. The function of theabove-described embodiment is implemented by executing a loaded program.In addition, the function of the present invention may be implemented byperforming processing in conjunction with an operating system or anotherapplication program or the like on the basis of an instruction of theprogram.

In the case of circulating the program in the market, the program may becirculated by being stored in a portable recording medium or by beingtransferred to a server computer connected via a network, such as theInternet. In this case, a storage device of the server computer is alsoincluded in the present invention. Part or all of the mobile stationapparatuses 5 and the base station apparatus 3 according to theabove-described embodiment may be typically implemented as an LSI, whichis an integrated circuit. The individual functional blocks of the mobilestation apparatuses 5 and the base station apparatus 3 may beindividually mounted on chips, or some or all of the functional blocksmay be integrated into a chip. The integration method is not limited tothe LSI, and an integrated circuit may be formed of a dedicated circuitor a multi-purpose processor. In a case where an integration technologythat replaces the LSI emerges due to progress of the semiconductortechnology, an integrated circuit produced based on the technology canbe used. The individual functional blocks of the mobile stationapparatuses 5 and the base station apparatus 3 may be formed of aplurality of circuits.

Information and signals can be indicated by using various differenttechnologies and method. For example, a chip, a symbol, a bit, a signal,information, a command, an instruction, and data that can be referred tothrough the description given above can be indicated by a voltage, acurrent, an electromagnetic wave, a magnetic field or magnetic particle,an optical field or optical particle, or a combination of them.

Various exemplary logical blocks, processing units, and algorithm stepsdescribed above in association with the disclosure of this descriptioncan be mounted as electronic hardware, computer software, or acombination of both. To clearly express the synonymity of hardware andsoftware, various exemplary elements, blocks, modules, circuits, andsteps have been described about their functionality. Whether suchfunctionality is installed as hardware or software depends on designrestrictions on individual applications and the entire system. A personskilled in the art can install the above-described functionality byusing various methods for individual specific applications, but decisionof such installation should not be interpreted as deviation from thescope of the present disclosure.

Various exemplary logical blocks and processing units described above inassociation with the disclosure of this description can be installed orimplemented by a multi-purpose processor, digital signal processor(DSP), application specific integrated circuit (ASIC), and fieldprogrammable gate array signal (FPGA) that are designed to execute thefunctions described in this description, or another programmable logicaldevice, a discrete gate or transistor logic, a discrete hardwarecomponent, or a combination of them. The multi-purpose processor may bea microprocessor. Instead, the processor may be a conventionalprocessor, a controller, a microcontroller, or a state machine.Alternatively, the processor may be installed in combination with acomputing device. The combination may be, for example, a combination ofa DSP and a microprocessor, a combination of a plurality ofmicroprocessors, one or more microprocessors connected to a DSP core, ora combination of other configurations.

The method or algorithm steps described above in association with thedisclosure of this description can be directly embodied by hardware, asoftware module implemented by a processor, or a combination of them.The software module can exist in a RAM memory, a flash memory, a ROMmemory, an EPROM memory, an EEPROM memory, a register, a hard disk, aremovable disc, a CD-ROM, or recording media in various formats that areknown in this field. A typical recording medium can be coupled to aprocessor so that the processor can read information from the recordingmedium and can write information on the recording medium. In anothermethod, the recording medium may be incorporated into the processor. Theprocessor and the recording medium may be in an ASIC. The ASIC can be ina mobile station apparatus (user terminal).

Alternatively, the processor and the recording medium may be in themobile station apparatus 5 as discrete elements.

In one or more typical designs, the functions described above can beinstalled as hardware, software, firmware, or a combination of them. Ifthe functions are installed as software, the functions can be stored ortransmitted as one or more instructions or codes on a computer-readablemedium. The computer-readable medium includes a communication medium anda computer recording medium, which include a medium that helps carryingof a computer program from a certain place to another place. A recordingmedium may be any commercially available medium that can be accessed bya multi-purpose or application-specific computer. Examples of such acomputer-readable medium include a RAM, a ROM, an EEPROM, a CDROM, oranother optical disc medium, a magnetic disk medium or another magneticrecording medium, or a medium usable for carrying or holding desiredprogram code means in the form of an instruction or a data structure andin the form of being accessible by a multi-purpose orapplication-specific computer or a multi-purpose or application-specificprocessor. The computer-readable medium is not limited to theseexamples. Various forms of connection are appropriately calledcomputer-readable media. For example, in a case where software istransmitted from a website, a server, or another remote source by usinga coaxial cable, an optical fiber cable, a twisted pair, a digitalsubscriber line (DSL), or a wireless technology such as infrared, radio,or microwaves, the coaxial cable, optical fiber cable, twisted pair,DSL, or the wireless technology such as infrared, radio, or microwavesare included in the definition of a medium. The disc or disk used inthis description includes a compact disc (CD), a laser disc (registeredtrademark), an optical disc, a digital versatile disc (DVD), a floppy(registered trademark) disk, and a blue-ray disc. Generally, data ismagnetically played back from a disk, whereas data is optically playedback from a disc using laser. A combination of the above-described mediashould also be included in the computer-readable medium.

The embodiment of the present invention has been described in detailabove with reference to the drawings. The specific configuration is notlimited to the embodiment, and design or the like within the gist of thepresent invention is also included in the claims.

REFERENCE SIGNS LIST

-   -   3 base station apparatus    -   4 (A-C) RRH    -   5 (A-C) mobile station apparatus    -   101 reception processor    -   103 radio resource controller    -   105 controller    -   107 transmission processor    -   109 receive antenna    -   111 transmit antenna    -   201 physical downlink shared channel processor    -   203 physical downlink control channel processor    -   205 downlink pilot channel processor    -   207 multiplexer    -   209 IFFT unit    -   211 GI insertion unit    -   213 D/A unit    -   215 transmission RF unit    -   219 turbo encoder    -   221 data modulator    -   223 convolutional encoder    -   225 QPSK modulator    -   227 precoding processor (for PDCCH)    -   229 precoding processor (for PDSCH)    -   231 precoding processor (for downlink pilot channel)    -   301 reception RF Unit    -   303 A/D unit    -   309 symbol timing detector    -   311 GI remover    -   313 FFT unit    -   315 subcarrier demapping unit    -   317 channel estimator    -   319 channel equalizer (for PUSCH)    -   321 channel equalizer (for PUCCH)    -   323 IDFT unit    -   325 data demodulator    -   327 turbo decoder    -   329 physical uplink control channel detector    -   331 preamble detector    -   333 SRS processor    -   401 reception processor    -   403 radio resource controller    -   405 controller    -   407 transmission processor    -   409 receive antenna    -   411 transmit antenna    -   501 reception RF Unit    -   503 A/D unit    -   505 symbol timing detector    -   507 GI remover    -   509 FFT unit    -   511 demultiplexer    -   513 channel estimator    -   515 channel compensator (for PDSCH)    -   517 physical downlink shared channel decoder    -   519 channel compensator (for PDCCH)    -   521 physical downlink control channel decoder    -   523 data demodulator    -   525 turbo decoder    -   527 QPSK demodulator    -   529 Viterbi decoder    -   531 downlink reception quality measurement unit    -   533 PDCCH demapping unit    -   605 D/A unit    -   607 transmission RF unit    -   611 turbo encoder    -   613 data modulator    -   615 DFT unit    -   617 uplink pilot channel processor    -   619 physical uplink control channel processor    -   621 subcarrier mapping unit    -   623 IFFT unit    -   625 GI insertion unit    -   627 transmit power adjuster    -   629 random access channel processor    -   2101 to 2112 region    -   2151 to 2155 E-CCE    -   2201 to 2208 region    -   2251 to 2254 E-CCE    -   2301 to 2312 region    -   2351 to 2362 E-CCE    -   2401 to 2406 PRB pair    -   2501 to 2506 PRB pair    -   2601 to 2606 PRB pair    -   2701 to 2706 PRB pair    -   2801 to 2806 PRB pair

1. A terminal apparatus comprising: a receiver configured to and/orprogrammed to monitor a set of enhanced physical downlink controlchannel candidates according to downlink control information format; acontroller configured to and/or programmed to select a value set from aplurality of value sets on the basis of at least the downlink controlinformation format, wherein the sets of enhanced physical downlinkcontrol channel candidates include a plurality of enhanced physicaldownlink control channel candidates associated with a plurality ofAggregation Levels, each of the plurality of Aggregation Levelscorresponds to a value in the value set.
 2. A base station apparatuscomprising: a controller configured to and/or programmed to select avalue set from a plurality of value sets on the basis of at least adownlink control information format of a downlink control information; atransmitter configured to and/or programmed to transmit an enhancedphysical downlink control channel that carries the downlink controlinformation by using the downlink control information format, whereinthe enhanced physical downlink control channel associated with anAggregation Level, the Aggregation Level corresponds to a value in thevalue set.
 3. A communication method of a terminal apparatus comprising:monitoring a set of enhanced physical downlink control channelcandidates according to downlink control information format; selecting avalue set from a plurality of value sets on the basis of at least thedownlink control information format, wherein the sets of enhancedphysical downlink control channel candidates include a plurality ofenhanced physical downlink control channel candidates associated with aplurality of Aggregation Levels, each of the plurality of AggregationLevels corresponds to a value in the value set.
 4. A communicationmethod of a base station apparatus, comprising: selecting a value setfrom a plurality of value sets on the basis of at least a downlinkcontrol information format of a downlink control information;transmitting an enhanced physical downlink control channel that carriesthe downlink control information by using the downlink controlinformation format, wherein the enhanced physical downlink controlchannel associated with an Aggregation Level, the Aggregation Levelcorresponds to a value in the value set.